Two US warships were passing through the Suez Canal on their way to waters off Libya on Wednesday as Western nations exerted diplomatic and military pressure on Muammar Gaddafi to step down.

The United States said Libya could sink into civil war unless the Libyan leader ends his four-decade rule amid fears that the uprising, the bloodiest yet against long-serving rulers
in the Middle East, could cause a humanitarian crisis.
   
Gaddafi is defiant and his son, Saif al-Islam, has warned the West against launching military action. He said the veteran ruler would not relinquish power or be driven into exile.   

Across Libya, tribal leaders, officials, military officers and army units have defected to the rebel cause and say they are becoming more organised. Tripoli is a stronghold for Gaddafi in this oil-producing north African state.

'We are going to keep the pressure on Gaddafi until he steps down and allows the people of Libya to express themselves freely and determine their own future,' Susan Rice, the US ambassador to the United Nations, told ABC's 'Good Morning America'.   

Captain Faris Zwei, among officers in the east who joined the opposition to Gaddafi, said there were more than 10,000 volunteers in Ajdabiyah, 800 km (500 miles) from the capital.   

'We are reorganising the army, which was almost completely destroyed by Gaddafi and his gang before they left,' he said. 'We are reforming, as much as we can, the army from the youth that took part in the revolution.'

Two amphibious assault ships, USS Kearsarge, which can carry 2,000 Marines, and USS Ponce, entered the canal on Wednesday en route to the Mediterranean. The destroyer USS Barry moved  through the Suez Canal on Monday.

The ships entered through the southern end of the canal, an official said, adding that they were expected to pass through by 3:30 pm (1330 GMT) or 4:00 pm local time.

Arab League foreign ministers meet on Wednesday at an extraordinary session in Cairo and are expected to reinforce their condemnation of Gaddafi. Some delegates want the meeting to underline the League's unwillingness to see foreign intervention in Libya.    

The repositioning of US ships and aircraft closer to Libya is widely seen as a symbolic show of force since neither the United States nor its NATO allies have shown any appetite for direct military intervention in the turmoil that has seen Gaddafi lose control of large swaths of his country.   - Reuters