The U.S. and its allies intensified air attacks against forces loyal to Col. Moammar Gadhafi on Sunday, keeping anti-Gadhafi rebels from being immediately overrun and bringing a reprieve to the increasingly desperate pro-democracy uprising.

Allied jets and missiles pounded Libyan military targets over the weekend, including one of Col. Gadhafi’s armored columns seen charred on the road to Benghazi, the rebels’ de facto capital. Rebels emboldened by the international support renewed fighting in Ajdabiya, a strategic city they had lost last week, witnesses said.

On Sunday night, fighter jets were heard above the center of Tripoli, followed by explosions and antiaircraft fire a witness said struck military installations. Later, Libyan authorities said a building in Col. Gadhafi’s compound had been hit and damaged.

National Security Adviser Thomas Donilon told reporters traveling with President Barack Obama in Brazil that “the efforts here have made a real difference in terms of the threat that was looming over Benghazi.”

Mr. Donilon said U.S. officials and Libyan rebel leaders believe the military actions “have prevented what could have been a catastrophe at Benghazi.”

Despite what appeared to be a just-in-time rescue for the rebellion, there were still concerns that regime ground forces could infiltrate Benghazi in a way that the coalition couldn’t counter from the air.

U.S. Republicans criticized Mr. Obama for moving too slowly and demanded the president clarify what the mission was intended to achieve and how it would do so. House Speaker John Boehner of Ohio joined in the criticism.

There were also hints of unease in the international coalition that had come together last week around a United Nations resolution authorizing military action to protect Libyan civilians from their leader.

The head of the Arab League, a group whose endorsement of a no-fly zone gave political cover for U.S. and European action in a Muslim country, criticized the airstrikes as outside of the U.N. mandate.

China, meanwhile, “expressed regret” over the use of military force even as it decided last week not to block authorization of the strikes at the U.N. China’s rare acquiescence moved it further away from its longstanding foreign policy based on nonintervention.

The air assault, led by the U.S., France and Britain, provoked a confused response from the Libyan regime, with the colonel vowing to “exterminate” his opponents and his men seizing—then releasing—an Italian ferry in Tripoli, while his military announced a second cease-fire late in the day Sunday.

Libyan state media, quoting Libyan health officials, reported that at least 64 people have been killed and more than 150 wounded in airstrikes since Saturday, mostly civilians. Reporters were unable to verify the allegations. Western journalists escorted to what Libyan officials said were to be burials of two-dozen bombing victims were only able to confirm the burials of a 3-year-old girl and a man, who relatives said had died in the airstrikes.

While Mr. Obama and European leaders have called on Col. Gadhafi to leave office, the U.N. authorized force only to protect civilians. U.S. commanders are counting on the air attacks and no-fly zone to spark an uprising in Col. Gadhafi’s inner circle.

Obama administration officials and military commanders haven’t explained what would happen if Col. Gadhafi instead consolidated power in areas he already holds.

U.S. Defense Secretary Robert Gates told reporters Sunday afternoon he wouldn’t want to see Libya permanently split into government and rebel zones.

“Having states in the region begin to break up because of internal differences I think is a formula for real instability in the future,” Mr. Gates said during a flight to Russia for security talks.

He said he was skeptical of suggestions that the coalition expand its goals from defending civilians against Col. Gadhafi to killing the Libyan leader. “This is a very diverse coalition and the one thing that there is common agreement on are the terms set forth in this Security Council resolution,” Mr. Gates said. “If we start adding additional objectives, then I think we create a problem in that respect.”

The French government said that while on Saturday its jets had destroyed four Libyan armored vehicles, the 15 planes it had in Libyan airspace on Sunday had encountered no opposition.

“He’s got his forces pretty well stretched from Tripoli all the way out to Benghazi, and we will endeavor to sever his logistics support in the next day or so,” the top U.S. military officer, Adm. Mike Mullen, told CNN’s “State of the Union” on Sunday.

In Tripoli, Col. Gadhafi vowed to arm civilians with machine guns, rifles, grenades and rocket launchers.

“We will exterminate every traitor and collaborator with America, Britain, France and the crusader coalition,” he said on state TV Sunday. “They shall be exterminated in Benghazi or any other place.”

At 9 p.m. in Tripoli, though, Col. Milad Hussein, a Libyan military spokesman, read a terse statement announcing an “immediate cease-fire,” shortly after fighter jets were heard above the center of the capital, followed by several explosions and a barrage of antiaircraft fire.

A resident of Tripoli’s eastern suburb of Tajoura said it appeared the latest strikes hit military installations in the neighborhoods of Farnaj or Ain Zara. At 10 p.m. Libya time, explosions could be heard in the capital followed by salvos of antiaircraft fire and machine guns, this time close to Col. Gadhafi’s compound in Bab Aziziya.

Late Sunday, two missiles hit a building inside Col. Gadhafi’s compound, said Libyan officials who took foreign journalists to the scene. The officials wouldn’t say whether the Libyan leader was present at the time.

“I can confirm that these strikes are not U.S. strikes,” a U.S. military official said.

Asked about reports that Col. Gadhafi’s compound had been hit, U.S. Vice Adm. William Gortney said, “At this particular point, I can guarantee that he’s not on our targeting list,” and that Col. Gadhafi’s residence wasn’t targeted. But he added: “If he happens to be in a place, if he’s inspecting a surface-to-air missile site, we don’t have any idea that he’s there or not.”

Col. Hussein refused to take questions from reporters, but the credibility of the latest cease-fire was doubtful, given that the regime had flouted a previous one announced on Friday, nearly crushing the rebellion before the allies took action.

With the exception of Col. Gadhafi’s supporters in their cars honking their horns and waving banners and posters, the mood in Tripoli was subdued earlier Sunday. Although Sunday is the first day of the work week here, most shops were shuttered and there were long lines outside bakeries and gasoline stations.

Officials bused reporters to the Shatt Hansheer cemetery on Tripoli’s seashore for what was supposed to be a burial ceremony for victims of the airstrikes. Hundreds of pro-Gadhafi supporters gathered at the cemetery gate waving posters of the leader while men fired their weapons in the air.

Inside a few dozen men formed a human chain around 24 freshly dug graves. There were six other graves dug up nearby.

Several of those in attendance, diehard Gadhafi supporters, said the graves were for soldiers killed in the airstrikes. Many of them were killed in airstrikes against a base for the 32nd Brigade in Tripoli’s sprawling al-Hadhba neighborhood, said Youssef Mohammed who lives nearby.

As the men waited, they recited verses from the Quran and chanted slogans against the rebels and Arab countries they said were conspiring against Libya.

By sunset, coffins of the dead soldiers hadn’t arrived. People started leaving the cemetery.

After the strike hit the Bab Azizya compound, angry followers of Col. Gadhafi picked through piles of concrete and twisted steel for what they said were pieces of the missiles.

“They are dreaming if they think they can harm him. He’s in the heart of every Libyan,” said one of the hundreds of soldiers guarding the compound, which resembles a military barrack.

French fighter jets spearheaded the international military action Saturday, followed by a salvo of 124 cruise missiles fired from U.S. and U.K. warships. The cruise-missile attacks were aimed at radar, surface-to-air missile launchers and communications infrastructure so a broader no-fly zone could be enforced over Libyan airspace.

With air defenses damaged, the air war quickly expanded. On Saturday night, three U.S. B-2 stealth bombers, flying nonstop from an airbase in Missouri, bombed an airfield at Ghardabiya, not far from Misrata, Libya’s third-largest city.

Ghardabiya is both a military and civilian facility, and On Sunday, the Libyan government shelled Misrata, Libya’s third-largest city, witnesses said. A spokesman for the revolutionaries in Misrata said in a call to al-Jazeera television that government tanks have entered deep into that city’s center, hunting down besieged rebels.

Adm. Gortney told reporters in a Pentagon briefing Sunday that the bombers only targeted military portions of the airfield. He pointed to poststrike images that indicated damage to hardened aircraft shelters.

In addition to the B-2 strikes, coalition aircraft launched attacks on loyalist ground forces about 10 miles south of Benghazi. U.S. Air Force and Marine Corps strike aircraft, along with warplanes from France and the United Kingdom, participated in the attacks. According to a Pentagon briefing, the targets included armor, rocket launchers and mechanized infantry.

Qatar became the first Arab nation to join international action against Col. Gadhafi, saying on Sunday that it was sending fighter jets to Libya to help enforce the U.N. resolution. The French Defense Ministry said Sunday it expected four Qatari Mirage 2000 jets to fly over Libya.

At the purported funeral in Tripoli, one angry man said Libya should attack Qatar. “Let’s kill the Qatari people,” said Khalid Salem Anbia, 32 years old. “For every one of our martyrs, we will take 20-30 Qataris.”

The U.S., France and other Western members of the international coalition have said explicit support—and possible contributions—by Arab nations would be crucial to avoiding the perception that Libya could become the center of yet another clash between the West and an Arab, Islamic nation.

Mr. Gates said the U.S. has “received strong indications from several Arab states that they would participate.”

Indeed, U.S. officials from the president on down made clear over the weekend that U.S. military action—such as cruise-missile strikes to destroy Col. Gadhafi’s ability to shoot at allied planes—was intended to allow other countries to take the lead against the Libyan regime. Gen. Carter Ham, the head of U.S. Africa Command, is the senior U.S. commander supervising the operation, but defense officials say he is in the process of sorting how the operation would be handed over to coalition control in the coming days.

At least one fissure has surfaced within the international coalition, however. “What has happened in Libya differs from the goal of imposing a no-fly zone and what we want is the protection of civilians and not bombing other civilians,” Amr Moussa, secretary-general of the 22-nation Arab League, told reporters in Cairo. He said he was calling for an emergency meeting of the Arab League to discuss the situation in Libya, although it wasn’t clear when such a gathering would take place.

Mr. Moussa is expected to step down soon from his position and stand as a presidential candidate in Egypt, which is likely to hold elections later this year. There was speculation in Egypt on Sunday that his comments were mainly directed at a domestic audience; the Islamist and largely anti-Western Muslim Brotherhood is considered a major potential electoral power in Egypt.

—David Gauthier-Villars, Alistair MacDonald, Matthew Rosenberg, Laura Meckler, Adam Entous and Alan Zibel contributed to this article.