The official, speaking on condition of anonymity, confirmed the deployment of the guided-missile destroyer but declined to say that the show of force was meant for Syria or Iran, which Washington considers foes of Lebanese democracy.

It is "a show of support for regional stability" because of "concern about the situation in Lebanon," the official said.

The guided missile destroyer USS Cole was the target of a bombing by Al-Qaeda extremists in October 2000 in the Yemeni port of Aden that killed 17 US sailors.

Asked whether US President George W. Bush had given the order, White House spokesman Gordon Johndroe said: "The president is concerned about the situation in Lebanon and discusses the issue regularly with his national security team."

Lebanon's presidential vacuum has entered its fourth month with no resolution in sight, fueling fears that a deepening sectarian rift could stoke civil strife.

Arab leaders have stepped up efforts to bridge the divide between the Western-backed ruling coalition and the opposition supported by Syria and Iran, but analysts said they do not hold out much hope of a deal ahead of an Arab summit next month.

Recent street clashes between supporters of rival factions have further raised tensions and prompted several Gulf nations and Western states to advise their citizens against traveling to Lebanon.

Saudi Foreign Minister Prince Saud al-Faisal even warned earlier this month that the country was "on the verge of civil war."

Adding to the tension, Hezbollah chief Hassan Nasrallah has vowed "open war" against Israel, blaming it for the February 12 car-bombing death in Damascus of Hezbollah top commander Imad Mughnieh, which Israel welcomed but denied any involvement in.

Lebanon has been without a president since November 24 when Damascus protege Emile Lahoud stepped down in the midst of the worst political crisis since the country's 1975-1990 civil war.

Analysts say plans for an international tribunal to try the assassins of former prime minister Rafiq Hariri, who was close to Saudi Arabia, is another source of the tension.

Syria is widely blamed for the February 2005 killing of Hariri in a massive Beirut car bombing but Damascus has denied any involvement.

However, two months after the murder, Syria pulled out its troops from Lebanon under domestic and international pressure, ending a 29-year military domination of its neighbor.