David Cameron and Barack Obama are 'preparing for what might have to be done if Gaddafi goes on brutalising his own people' as Lindsey Hilsum reports from the frontline.

Libya map: the flashpoints as Gaddafi hits back at rebels.

The international community cannot "stand aside" and allow brutal repression to continue in Libya, David Cameron has said after discussing plans for the "full spectrum of possible responses" including a no-fly zone with US President Obama.

Downing Street said the two leaders had agreed to "press forward" with possible measures as the offensive against rebels intensified with the regime employing rockets, tanks and military aircraft in a bid to end the uprising.

Mr Cameron said he was determined to "prepare for what we might have to do if he (Gaddafi) goes on brutalising his own people".

"I had a phone call with President Obama this afternoon to talk about the planning we have to do in case this continues and in case he does terrible things to his own people.

"I don't think we can stand aside and let that happen," he said.

A Number 10 said: "The Prime Minister and the President agreed to press forward with planning, including at Nato, on the full spectrum of possible responses, including surveillance, humanitarian assistance, enforcement of the arms embargo, and a no fly zone,"

Sir Richard Dalton, former British Ambassador to Libya and an expert in Middle East and North Africa relations, said military action needed unanimous support.

"It has to have legitimacy, otherwise it would be better not to do it, it will need a full degree of support. In today's world what constitutes a full degree of support will be a United Nations resolution or a wide consensus of relevant parties," he told Channel 4 News.

"If, as it has been suggested, Russia would never sign it, then a consultation in the region, and agreement between states in North Africa, North America, Latin America and Europe could go in as a military consensus."

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Anti-Gaddafi witnesses say forces loyal to the Libyan leader are using rockets, tanks and warplanes to attack them in Ras Lanuf and Zawiyah. Lindsey Hilsum reports from the frontline.

Fighting is continuing in Libya as rebels hold out against Colonel Gaddafi, who has been in power for more than 40 years.

On Tuesday, rebels said they were holding the town of Zawiyah, 30 miles west of Tripoli, despite attacks by forces loyal to the Libyan leader using tanks and aircraft.

Between 40 and 50 tanks were assaulting the town, backed up by 120 pick-up trucks with soldiers, and sporadic air strikes.

Local residents were reporting snipers along the main road into town and women and children cowering in damaged buildings in the centre.

In Ras Lanuf, an oil port in the east of Libya, rebels said they could not match Gaddafi's firepower as the battle continued. Government forces have made their base for attacks at Bin Jawad, a town about 40 miles away along the coast, and mounted fierce attacks on Ras Lanuf.

People are dying out there. Gaddafi's forces have rockets and tanks. Witness in Ras Lanuf

Gaddafi's forces attacked with tanks, rockets and warplanes, mounting at least four air strikes on the town. One witness, Abdel Salem Mohamed, said: "People are dying out there. Gaddafi's forces have rockets and tanks."

The rebels are armed as well - with machine guns, rocket propelled grenade launchers and anti-tank and anti-aircraft weaponry. But they say their weaponry is feeble compared to Gaddafi's.

Read more: a million children in 'real danger' in western Libya

No deaths have been reported in the fighting yet but hospitals are taking in the wounded.

Air strikes in Ras Lanuf have hit residential areas, rebels said. Many civilians have already evacuated the area as the fighting intensifies, and the rebels have also moved their weapons to the desert over fears of a Government-led ground attack.

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Channel 4 News International Editor Lindsey Hilsum, in Ras Lanuf, said: "This is the last rebel checkpoint before no-man's land. The rebels are making forays into that area and there's skirmishes further ahead, but they don't seem to be making much progress.

"They've been here for a couple of days now. It seems like stalemate."

She reported hearing four bombings in Ras Lanuf, and witnessing anti-aircraft fire from rebels, who described the situation to her as "hit and run". But they remain "resolute in the belief that God and history are on their side," she said.

Fighting

The two towns, Zawiyah and Ras Lanuf, have become the frontline of the fighting after battles over the weekend in other locations. Colonel Gaddafi remains in control of Tripoli while the rebels are strong in the east of the country, particularly in Benghazi.

Read more in the Channel 4 News Special Report on the Arab revolts

Hafiz Ghoga, spokesman for the rebel National Libyan Council, told a news conference in Benghazi: "We already prevailed and we will complete our victory when we are afforded a no-fly zone. If there was also action to stop him [Gaddafi] from recruiting mercenaries, his end would come within hours."

When asked if the revolutionaries would take US arms, Mr Ghoga said: "Our slogan was the downfall of the oppressive regime. When the regime confronted the youth with live ammunition it was only natural for them to defend themselves. We still consider our revolution a peaceful one. The youth are defending themselves and the revolution."

Rumours that Gaddafi was considering stepping down were dismissed as "nonsense" by the Government in Tripoli.

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