US warships will pass through the Suez Canal on Wednesday on their way to Libya as Western nations put more pressure on Muammar Gaddafi to stop a violent crackdown and step aside.

The United States said Libya could sink into civil war unless Gaddafi quits amid fears that the uprising, the bloodiest against long-serving rulers in the Middle East, could cause a humanitarian crisis.

Gaddafi remained defiant and his son, Saif Al-Islam, warned the West against launching military action. He said the   veteran ruler would not step down or go into exile.     

Italy said it was sending a humanitarian mission to neighbouring Tunisia to provide food and medical aid to as many as 10,000 people who had fled violence in Libya on its eastern border.

Tunisian border guards fired into the air on Tuesday to try to control a crowd of people clamouring to cross the frontier.     
About 70,000 people have passed through the Ras Jdir border post in the past two weeks, and many more of the hundreds of thousands of foreign workers in Libya are expected to follow.

 'Using force against Libya is not acceptable. There's no reason, but if they want ... we are ready, we are not afraid,' Saif al-Islam told Sky television.

US Secretary of State Hillary Clinton told US lawmakers: 'Libya could become a peaceful democracy or it could face protracted civil war.'

The United States said it was moving ships and planes closer to the oil-producing North African state. The destroyer USS Barry moved through the Suez Canal on Monday and into the Mediterranean. Two amphibious assault ships, the USS Kearsarge, which can carry 2,000 Marines, and the USS Ponce, were in the Red Sea and are expected to go through the canal early on Wednesday.       

The White House said the ships were being redeployed in preparation for possible humanitarian efforts but stressed it  'was not taking any options off the table'.

'We are looking at a lot of options and contingencies. No decisions have been made on any other actions,' US Defense   Secretary Robert Gates said.

French Foreign Minister Alain Juppe sounded a note of caution, saying military intervention would not happen without a clear United Nations mandate.     

British Prime Minister David Cameron, who said Britain would work with allies on preparations for a no-fly zone in Libya, said it was unacceptable that 'Colonel Gaddafi can be murdering his own people using airplanes and helicopter gunships'.     

General James Mattis, commander of US Central Command, told a Senate hearing that imposing a no-fly zone would be a 'challenging' operation. 'You would have to remove air defence capability in order to establish a no-fly zone, so no illusions here,' he said. 'It would be a military operation.'     

Analysts said Western leaders were in no mood to rush into the conflict after drawn-out involvements in Afghanistan and Iraq.

Gaddafi, a survivor of past coup attempts, told the US ABC network and the BBC on Monday: 'All my people love me,'   dismissing the significance of a rebellion that has ended his control over much of oil-rich eastern Libya.

Rebel fighters said the balance of the conflict was swinging their way. 'Our strength is growing and we are getting more weapons. We are attacking checkpoints,' said Yousef Shagan, a spokesman in Zawiyah, 50 km (30 miles) from Tripoli.

A rebel army officer in the eastern city of Ajdabiyah said rebel units were becoming more organized. 'All the military councils of Free Libya are meeting to form a unified military council to plan an attack on Gaddafi security units, militias and mercenaries,' Captain Faris Zwei said.

He said there were more than 10,000 volunteers in the city, plus defecting soldiers.

The New York Times reported that the rebels' revolutionary council was debating whether to ask for Western air strikes on  some of Gaddafi's military assets under a United Nations banner.

The Times said Abdel-Hafidh Ghoga, the council's spokesman, declined to comment on its deliberations but said: 'If it is with the United Nations, it is not a foreign intervention,' which the rebels have said they oppose. - Reuters