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A missile strike has destroyed a building in Libya's capital, Tripoli, which Western officials say was one of Col Muammar Gaddafi's command centres.
Journalists were shown the wrecked building but it was not clear if there were any casualties.
Countries including the US, UK and France are continuing strikes after the UN authorised action to protect Libyan civilians from government forces.
Col Gaddafi has been fighting a rebellion that broke out last month.
US and UK officials say Col Gaddafi himself is not a target of the air strikes, which they insist are aimed at his troops and air defence systems.
The chief of the UK defence staff, Gen Sir David Richards, told the BBC that targeting the Libyan leader was "not allowed under the UN resolution".
A Libyan official said 64 people had been killed in strikes at the weekend, but the figure could not be verified.
On Sunday night anti-aircraft fire rose over Tripoli and several explosions were heard. A BBC reporter saw a column of smoke rising from the direction of Bab al-Aziziya, where Col Gaddafi has his military base and compound.
Western journalists taken by Libyan officials to the compound were shown a ruined three or four-storey building. It is not clear whether Col Gaddafi was there at the time of the bombing.
An official from one of the coalition countries, who asked not to be named, told journalists the strike had destroyed Col Gaddafi's "command and control capability".
Earlier at the Pentagon, US Navy Vice Adm William Gortney said the coalition had control of the air space between Tripoli and the main rebel stronghold, Benghazi in the east. "The no-fly zone is effectively in place," he said.
He added that ground forces moving on rebel positions were also open to attack.
In Misrata, a city west of Benghazi that has been under siege by government troops, residents say bombardments by pro-Gaddafi forces are continuing. A nearby air base was targeted in the first night of coalition strikes.
The BBC's Kevin Connolly, in the rebel-held city of Tobruk, says it is not clear if the allies can attack Col Gaddafi's troops operating in the centre of Misrata without harming the very civilians they have come to save.
A rebel spokesman told Reuters news agency that pro-Gaddafi forces were bringing civilians to Misrata from outlying areas to deter further allied strikes.
On Monday Britain said it had called off an air raid during the night because civilians were spotted near the target area. The UK defence ministry did not say where the planned target had been.
Arab League Secretary General Amr Moussa, who supported the UN resolution, on Sunday 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," he said.
But on Monday, in a joint news conference with visiting UN Secretary General Ban Ki-moon in Cairo, Mr Moussa played down any differences within the coalition. "We are all united on the issue of protecting civilians," he said.
Both he and Mr Ban stressed that Arab League support was a key factor in securing Security Council backing for the UN resolution.
In Benghazi, heavy gunfire and sporadic explosions were heard on Sunday night, a witness told Reuters news agency.
"Benghazi is not completely safe from attack but it is certainly under less threat than it was yesterday," he said.
The US says a Libyan government claim that armed forces were observing a ceasefire "isn't true or has been immediately violated".
The action against Col Gaddafi's military began on Saturday afternoon with French air strikes in the east. A barrage of cruise missiles, launched from US and UK ships and submarines followed.
US Defence Secretary Robert Gates has said that while the US will continue to play a part in operations against Col Gaddafi's forces, it "will not have the pre-eminent role".
Meanwhile, the build-up of forces to enforce the no-fly zone continues.
Qatar is to send four planes to join the coalition enforcing the UN-mandated no-fly zone, the US and France have said.
The move would make Qatar the first Arab country to play an active part in the campaign against Col Gaddafi.
Other Arab countries are also preparing to join the campaign against Col Gaddafi, Adm Gortney said.
The French aircraft carrier Charles de Gaulle has left the Mediterranean port of Toulon for Libya, while Denmark and Norway are each sending six planes. Spain has sent at least three planes, while Italy also has jets ready to deploy. Canada has deployed six jets to Sicily and is preparing them for action.
Col Gaddafi has ruled Libya for more than 40 years. An uprising against him began after the long-time leaders of neighbouring Tunisia and Egypt were toppled.