The United Nations seems on the brink of taking a momentous decision.

United Nations Security Council is due to meet in New York to discuss action in Libya.

Western countries want a no-fly zone to halt the advance of forces loyal to Libyan leader Col Muammar Gaddafi.

In recent days pro-Gaddafi forces have retaken several towns seized by rebels during an uprising.

Addressing the people of Benghazi, the rebels' main stronghold, Col Gaddafi said his troops were coming "tonight" and there would be "no mercy".

He told rebels to go home, adding that "whoever lays down his weapons" would be pardoned.

The US, UK and France are proposing a UN Security Council resolution backing action short of an invasion.

The United Nations seems on the brink of taking a momentous decision.

After hanging back for days, the Americans have now not only backed the British and French resolution on Libya but beefed it up.

The fact that French Foreign Minister Alain Juppe will be here in person is a sign of his confidence that the Russians and Chinese won't block it.

Some reports quote the French saying that there could be an attack within hours of a vote passing. It is likely five Arab air forces will take part.

Although there have been other recent UN operations, this would be the most serious intervention in a crisis for a long time, a marked contrast to the division over Iraq.

That does not ease the worries of some in the administration that this will still be labelled an American war and they will be dragged deeper and deeper into the affairs of another Arab nation.

Diplomatic sources say Russia and China - which often oppose the use of force against a sovereign country as they believe it sets a dangerous precedent - will abstain rather than using their power of veto.

They suggest that if the resolution is passed, air attacks on Col Gaddafi's forces by the British and French air forces could begin within hours. It is not thought that the US would be involved in the first strikes, but the British and French are likely to get logistical backup from Arab allies.