Western powers are discussing how to enforce a no-fly zone over Libya after the passage of a UN resolution backing “all necessary measures” to protect civilians, short of an occupation.
France said there could be air strikes “within hours”, though the details and timing of any action remain unclear.
Forces loyal to Col Muammar Gaddafi have been advancing eastwards towards the rebel stronghold of Benghazi.
They were also said to be bombarding the city of Misrata on Friday.
Col Gaddafi has promised to retake Benghazi, saying his forces would show “no mercy”.
Meanwhile, Libya has closed its airspace to all traffic, Europe’s air traffic control agency says.
Nato is due to discuss on Friday what role the alliance might play.
French government spokesman Francois Baroin said on Friday morning that strikes could take place “rapidly” and “within a few hours”. But he added: “You will understand that there’s no question of talking as early as this morning about when, how, which targets or in which form.”
It is not thought that the US would be involved in the first strikes. The British and French, along with some Arab allies, are expected to play a leading role. Norway has said it will also participate.
Qatar will take part in international efforts to protect civilians, Qatar’s official news agency reported, though it was not clear if this included military operations.
The UN resolution is so broad that it allows military action against all threats to civilians, and could involve bombing Col Gaddafi’s forces on the ground if deemed necessary.
Rebel forces in Benghazi reacted with joy to the UN resolution, but a government spokesman condemned UN “aggression”. One of Col Gaddafi’s sons, Saif al-Islam, said the resolution was “unfair” as Libya had not been bombing civilians.
Following the UN vote, US President Barack Obama called the French and British leaders to discuss the next move. They said Libya had to comply immediately with the resolution.