The USS Nimitz aircraft carrier is moving westward toward the Red Sea, although it has not yet received orders to support a potential US strike on Syria, ABC News reported Monday.

The Nimitz carrier strike group, which includes a guided missile cruiser and four destroyers, was kept in the Indian Ocean for a "prudent responsible decision," an official told the television channel.

A defense official confirmed to AFP that the carrier was in the region but declined to give a specific location.

"Overlap of Navy vessels is routine as responsibilities are passed and the number of ships in a given area of responsibility vary," the official said.

"However, we are preserving options by keeping some additional ships in the region to include the USS Nimitz aircraft carrier."

The nuclear-powered carrier was set to head back to its home port in Everett, Washington, after a months-long deployment to the Arabian Sea when it reportedly received orders to stay in the area.

But it has not been assigned a specific mission and defense officials described the move as "prudent positioning," according to ABC.

Five US destroyers are now positioned in eastern Mediterranean waters, up from the usual three that normally focus on countering Iranian ballistic missile threats to Europe.

The destroyers -- the USS Stout, Mahan, Ramage, Barry and Graveley -- are ready to fire cruise missiles if President Barack Obama gives the order.

The USS San Antonio, a Navy amphibious ship with several helicopters and hundreds of Marines on board, has also been ordered to be stationed in the eastern Mediterranean but a defense official said it has "received no specific tasking."

No amphibious landing is in the works, however, as Obama has ruled out any "boots on the ground" if the US takes military action against the Syrian regime.

In a surprise move, Obama has delayed the threat of missile strikes against Damascus that had appeared imminent, saying he would first seek formal approval from Congress.