British military forces are in action over Libya. The first shots of the conflict have been fired after Colonel Gaddafi’s troops pushed into Benghazi.

Speaking outside 10 Downing Street, Mr Cameron said the action being taken by international forces in Libya was “necessary, legal and right”.

He said his thoughts were with British service personnel who were risking their lives to save others.

And he said: “I believe we should all be confident that what we are doing is in a just cause and in our nation’s interest.”

Earlier, French fighter jets began the UN-authorised military action, firing on armoured vehicles being used by forces loyal to Gaddafi outside the rebel stronghold of Gaddafi.

No ceasefire

A Libyan rebel spokesman said Gaddafi’s forces had entered Behghazi on Saturday morning while a witness saw at least one explosion near the rebel movement’s headquarters in the city.

A jet appeared to have been shot down in spite of a declared ceasefire and a U.N. no-fly resolution.

Rebels said Libyan jets had bombed the road to Benghazi airport and elsewhere on the outskirts.

The Libyan government denied its forces were in action in or around Benghazi. A government spokesman said they were observing the ceasefire, blaming rebels for attacks.

The time for action has come. It needs to be urgent. David Cameron

Prime Minister David Cameron said: “Colonel Gaddafi has made this happen. He has lied to the international community, he has promised a ceasefire, he has broken that ceasefire.

“He continues to brutalise his own people and so the time for action has come. It needs to be urgent, we have to enforce the will of the United Nations and we cannot allow the slaughter of civilians to continue.”

Libya had declared a unilateral ceasefire on Friday after the U.N. Security Council authorised a no-fly zone over Libya.

Libyan rebels said they were being forced back by Gaddafi’s forces. Black plumes of smoke could be seen on the road to the west of the city.

Elsewhere in the city, rebels reported skirmishes and strikes by Gaddafi forces.

“Fighter jets bombed the road to the airport and there’s been an air strike on the Abu Hadi district on the outskirts,” Mohammed Dwo, a hospital worker and a rebel supporter, told Reuters.

He was speaking at the aftermath of an apparent firefight between rebels and men they claimed were two mercenaries who had infiltrated the city and had been driving a car which they said contained a crate of hand grenades.

The two men, in civilian clothes, had been shot dead and rebels produced blood-soaked identity papers they said showed them to be of Nigerian nationality.

“We were sitting here and we received gunfire from this vehicle then we opened fire and after that it crashed,” rebel fighter Meri Dersi said.

Misrata

Residents of the rebel-held Libyan city of Misrata said government snipers were shooting people from rooftops and the hospital could not operate on the wounded because it had no anaesthetic.

Misrata, about 200 km (130) miles east of Tripoli, is the last big rebel stronghold in the west of the country and people living there say forces loyal to Libyan leader Muammar Gaddafi are still trying to retake the city despite a ceasefire.

Local people said there was some shelling in the city on Saturday morning, though not as heavy as the previous day, and that the city was facing a humanitarian crisis because water supplies were cut for a third day.

“I am telling you, we are scared and we are alone,” a Misrata resident called Saadoun said.

“We have two people dead this morning, not because of the shelling but because there are snipers on some houses and they are shooting people, they are shooting whoever they see.”

“This morning there was some shelling from two tanks and it stopped but the destruction from yesterday’s bombardment is huge. Destruction every where. Mosques and houses; nothing was spared,” Saadoun said.

“We are all scared here, the people of Misrata are scared. We feel a humanitarian crisis is coming…(there is) no water for more than three days and no electricity.”

Reports from Misrata could not be verified independently because authorities in Tripoli have prevented journalists from reaching the city.

Libyan government officials deny attacking rebels and say they are observing a ceasefire.