BBC wrote:
Summit set to decide Libya action
Explosions have been heard in Libya's rebel-stronghold of Benghazi, despite a UN declaration of a no-fly zone.
A jet has been shot down over the city, the BBC's Ian Pannell reports from the city, amid heavy gunfire.
The rebels said they were under attack from pro-Gaddafi forces, but it is impossible to verify these reports.
Leaders from Britain, the US, France and Arab countries are due to meet in Paris to discuss military action in Libya under the new UN resolution.
The UN Secretary General says the world must "speak with one voice" on Libya.
The resolution authorised "all necessary measures" to protect Libyan civilians.
On Saturday, the rebels said they were being forced to retreat by Col Gaddafi's forces, who they said were just 20km (12.5 miles) outside Benghazi, Reuters reported, although it has not been possible to independently confirm reports of fighting.
Getting ready
Earlier, US President Barack Obama said pro-Gaddafi forces must stop attacking rebel areas or face military action.
"Gaddafi must stop his troops from advancing on Benghazi, pull them back from Ajdabiya, Misrata and Zawiya and establish water, electricity and gas supplies to all areas," he said on Friday.
But in line with the resolution, Mr Obama ruled out using US ground forces.
On Friday Col Muammar Gaddafi's government declared a unilateral truce but there were reports that government offensives in rebel-held towns were continuing.
The BBC's Ian Pannell in Benghazi, the main rebel-held city, says there were loud explosions to the west early on Saturday and a jet was seen flying overhead, but it was impossible to verify whether it was an attack by Col Gaddafi's forces.
Our correspondent says if this was such an attack it would be a very serious development and put more pressure on the international community to begin military action quickly.
Both sides have accused each other of breaking the ceasefire declared by Col Gaddafi's government.
The Security Council vote called for an immediate ceasefire and endorsed the use of force - including a no-fly zone aimed at preventing pro-Gaddafi forces from bombing rebel-held towns.
The British and French, along with some Arab allies, are expected to play a leading role in any initial air strikes.
The French ambassador to the UN, Gerard Araud, told the BBC that he expected military intervention within hours of Saturday's summit.
UK Prime Minister David Cameron - who is attending the meeting - has said British war planes are being moved to bases in the region.
"The clock is ticking and we must be ready to act quickly," said Mr Cameron.
Strength of outrage
Saturday's summit will be hosted by French President Nicolas Sarkozy. US Secretary of State Hillary Clinton will represent the Obama administration.
BBC diplomatic correspondent Bridget Kendall says it is a chance to demonstrate to the Gaddafi government, and to the rest of the world, the strength of outrage at his actions and the determination to stop him.
The US Navy is deploying additional warships to the Mediterranean to support possible military action.
The commander in charge of planning for the no-fly zone will be US Adm Samuel Locklear, the BBC's Mark Urban has learnt.
Denmark and Canada have said they will supply fighter jets, with Italy, Spain and France making air bases available.
Saudi Arabia, Qatar, the UAE and Jordan could be among Arab states taking part.
Nato is already providing 24-hour surveillance over Libya with its Awacs planes.
Secretary-General Anders Fogh Rasmussen said Nato was "completing its planning to be ready to take appropriate action in support of the UN resolution as part of the broad international effort."
The US ambassador to the UN, Susan Rice, told CNN that Col Gaddafi was already in violation of the UN Security Council resolution.
Col Gaddafi has ruled Libya for more than 40 years.
An uprising against him began last month after long-time leaders of neighbouring Tunisia and Egypt were toppled.
Al-Jazeera reported him on Friday as saying that the UN resolution was "blatant colonialism" that "does not have any justification".