Two United States amphibious assault ships have entered Egypt's Suez Canal on their way to the Mediterranean.
The US said earlier this week that it was moving ships and planes closer to Libya where a revolt against leader Muammar Gaddafi's rule is under way.
One of the ships can carry 2,000 Marines.
President Gaddafi is defiant and his son, Saif al-Islam, has warned the West against launching military action, adding that 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. However, attempts by government and anti-Gaddafi forces to finish one another off have been unsuccessful, leading to a stalemate.
The US says it is considering a ''full range of options'' to respond to the crisis.
US Defence Secretary Robert Gates acknowledged that warships and military aircraft were on standby but cautioned that they are unlikely to be used imminently.