French jets have launched a second day of operations over Libya to enforce a no-fly zone against Col Muammar Gaddafi's forces.
The 15 planes patrolled Libyan airspace but did not open fire because they met no resistance, a spokesman said.
Meanwhile, witnesses in the capital, Tripoli, reported a loud explosion. A plume of smoke was seen rising near Col Gaddafi's residence, AFP reported.
France also says Qatar is to about to deploy four planes to the operation.
The move would make Qatar the first Arab country to play an active part in the campaign against Col Gaddafi, who has been battling a month-long revolt.
In a statement from the Pentagon on Sunday, US Vice Admiral William Gortney said coalition raids were "judged to have been very effective" and no new Libyan air activity had been reported.
"Benghazi is not completely safe from attack but it is certainly under less threat than it was yesterday," he said.
"We believe his [Gaddafi's] forces are under considerable stress and suffering from isolation and a good deal of confusion."
The head of the Arab League, who supported the idea of a no-fly zone, has criticised the severity of the bombardment.
"What is happening in Libya differs from the aim of imposing a no-fly zone, and what we want is the protection of civilians and not the bombardment of more civilians," said Arab League Secretary General Amr Moussa.
Arab League support was a key factor in getting UN Security Council backing for the resolution authorising the move.
The BBC's Jonathan Head, in Cairo, says this looks like a worrying crack in the coalition. Western governments are counting on at least symbolic participation by the air forces of some Arab states, he adds.
In a news conference on Sunday, a Libyan military spokesman said its armed forces had ordered a ceasefire across the entire country, beginning at 2100 local time (1900 GMT).
However, the BBC's Allan Little in Tripoli says the government had been insisting that its troops were already observing a ceasefire order made on Friday.
Despite Friday's announcement, our correspondent adds, pro-Gaddafi troops have tried to enter Benghazi and have been in action at Misrata.
A rebel spokesman in Misrata told the BBC that pro-Gaddafi forces had launched fresh attacks on Sunday with heavy shelling.
Meanwhile, US military chief Adm Mike Mullen said the initial coalition raids on Libya on Saturday night had been "successful".
Allied forces fired more than 120 missiles against Libyan targets, mostly air defences, on Saturday night.
US fighter planes and B-2 stealth bombers were involved, Pentagon officials said.
Cruise missiles hit at least 20 air-defence sites in the capital, Tripoli, and the western city of Misrata, they said.
After an attack by French planes near the rebel-held city of Benghazi, some 14 bodies were lying near destroyed military vehicles, Reuters reported.
Libyan TV has broadcast footage it says showed some of the 150 people it claims were wounded in the attacks. It said 48 people had been killed. There was no independent confirmation of the deaths and Western officials said such claims should be treated with caution.
Meanwhile, the build-up of forces to enforce the no-fly zone continues. The French aircraft carrier Charles de Gaulle has left the Mediterranean port of Toulon for Libya.
Denmark and Norway are each sending six planes. Spain has sent at least three planes, plus a refuelling aircraft, while Italy also has jets ready to deploy.
A defiant Col Gaddafi promised Western powers "a long, drawn-out war with no limits" in a phone call to Libyan state TV on Sunday morning.
"We will fight inch by inch," he said while a sculpture of a golden fist crushing a US jet was being shown.
He said Western forces had no right to attack Libya, which had done nothing to them.
Col Gaddafi's son Saif al-Islam called Saturday's attack a "big mistake".
"Believe me, one day you will wake up and you will find out that you were supporting the wrong people and you had made a big mistake in supporting those people," he told Christiane Amanpour for ABC This Week. "It's like the WMD [weapons of mass destruction] in Iraq. It's another story."
Col Gaddafi earlier said he would open arms depots to the people to defend Libya and described the attacks as "crusader aggression".
Western forces began their actions on Saturday after pro-Gaddafi troops attacked the main rebel-held city of Benghazi.
Russia and China, which abstained from the UN Security Council resolution approving the use of force in Libya, have urged all parties to stop fighting, as has the African Union.
Col Gaddafi has ruled Libya for more than 40 years. An uprising against him began last month after the long-time leaders of neighbouring Tunisia and Egypt were toppled.