The US Navy has deployed a fifth destroyer to the eastern Mediterranean, a defense official told AFP on Thursday, as expectations grow of an imminent strike on Syria.

The USS Stout, a guided missile destroyer, is "in the Mediterranean, heading and moving east" to relieve the Mahan, said the official, who said both ships might remain in place for the time being.

Other destroyers in the region -- the Ramage, the Barry and the Gravely -- criss-cross the Mediterranean and could launch their Tomahawk missiles toward Syria if so directed by US President Barack Obama.

The defense official, speaking on condition of anonymity, did not say how long the Mahan would stay in the area before returning to its home port of Norfolk, Virginia, which it left in December 2012.

It is normal for three destroyers to patrol the Mediterranean under the authority of the US Sixth Fleet, primarily in an anti-missile defense role.

The US Navy keeps as a closely guarded secret the number of Tomahawk missiles that each ship carries but it is estimated to be 45.

Defense Secretary Chuck Hagel said on Wednesday that US forces were ready to launch an attack, but Obama said he has not yet made a decision.

The US defense official also indicated that the aircraft carrier USS Nimitz and its escorts remain in the area of the US Fifth Fleet, which extends from the Red Sea to the Gulf and Arabian Sea.

The official added, however, that while the Nimitz is being held, "it is not linked to potential Syria options at this time."