The destroyer USS Mahan has left the Mediterranean while a battle group of warships led by the aircraft carrier USS Nimitz is on its way to the Red Sea from the Indian Ocean, an official said.

The Mahan is "on its way to Norfolk," the ship's home port in Virginia, the defense official, who spoke on condition of anonymity, told AFP.

The departure of the Mahan reduced the number of US destroyers in the Mediterranean to four. Each of the warships is equipped to launch Tomahawk cruise missiles against targets in Syria if ordered to by US President Barack Obama.

The US Navy keeps secret the precise number of Tomahawks on board but most military analysts estimate each ship carries about 45 cruise missiles.

The Pentagon normally keeps three destroyers in the Mediterranean, under the command of the Navy's Sixth Fleet, with a mission primarily focused on missile defense.

The US military has also sent an amphibious transport ship, the USS San Antonio, to the region. The vessel, with helicopters and several hundred Marines, could be called in for any possible emergency evacuation of US diplomatic missions in the region.

The strike group led by the Nimitz aircraft carrier is meanwhile headed from the Indian Ocean to the Red Sea over "the next few days," the official said.

The carrier group would double the arsenal of Tomahawk missiles at Washington's disposal.

The strike group includes four destroyers, all equipped with cruise missiles, as well as a cruiser, the USS Princeton, which is also armed with the missiles.

NJF/NJF