In another "just in case" move by a Navy ship, the aircraft carrier USS Nimitz has moved into the Red Sea, but it has not been given orders to be part of the planning for a limited U.S. military strike on Syria, U.S. officials told ABC News.

A U.S. official confirmed that the Nimitz and four other ships moved into the Red Sea earlier today. The official said the carrier strike group has not been assigned a mission and the move to the Red Sea was a prudent move in case its resources are needed to "maximize available options". The other ships in the strike group are the cruiser USS Princeton and the destroyers USS William P. Lawrence, USS Stockdale and USS Shoup.

On Saturday, President Obama announced that he had decided upon military action against Syria, but that he would first seek authorization from Congress. Another U.S. official said that in the wake of that decision military planners are reviewing their options and force posture requirements in the region.

Last Wednesday, with the likelihood of a U.S. military action against Syria increasing, the USS Nimitz and four other ships in its strike group were kept in the Indian Ocean for what an official described as a "prudent responsible decision."

The carrier had just ended a months-long deployment to the Arabian Sea where its fighter aircraft had been providing air cover over Afghanistan. Having been replaced by the USS Harry S Truman, the carrier was expected to soon begin the trip home to its home port in Everett, Wash., when it received orders to linger in the area.

Defense officials told ABC News Sunday that the Nimitz was heading west, but added that it had not been assigned to a specific mission, so the move was just "prudent positioning."

Reuters was first to report Sunday that the Nimitz was moving westward towards the Red Sea. On Saturday, President Obama announced that he had decided upon military action against Syria, but that he would first seek authorization from Congress.

For now, U.S. officials have said any limited U.S. military action against Syria will likely come in the form of Tomahawk cruise missiles fired from Navy destroyers currently stationed in the eastern Mediterranean.

There are now five U.S. destroyers in the waters of the eastern Mediterranean, but even those numbers are the result of fortuitous timing. Typically, three Navy destroyers are stationed there to counter an Iranian ballistic missile threat to Europe.

Two of the destroyers were held over at the end of their deployments because of the dynamic situation in Syria and are now serving alongside the two destroyers that were slated to replace them.

On Friday, the USS San Antonio, a Navy amphibious ship with several hundred Marines aboard, was ordered to remain in the eastern Mediterranean though defense officials said it too was not part of the U.S. military planning for a limited strike against Syria. Defense officials described the move as "a prudent decision should the ship's capabilities be required.

The San Antonio was originally to be in the Mediterranean as part of a long-scheduled commitment to support U.S. Africa Command, several officials said. The ship was on its way to a port call at the U.S naval base at Souda Bay on the Greek Island of Crete when it was ordered to remain in the area.

The San Antonio has resources that could prove useful in future operations in the region. For example, the ship has several hundred Marines aboard from the 26th Marine Expeditionary Unit (MEU), as well as several helicopters or V-22 Ospreys that could be useful in helping to rescue downed pilots.

That scenario played out in the early days of the 2011 air assault on Libya when Marines from the 26th MEU aboard the amphibious ship USS Kearsarge rescued one of two F-15 pilots forced to eject after their fighter crashed outside Benghazi.

The San Antonio is one of three ships, carrying the 2,200 Marines of the 26th MEU aboard, that have been serving a six-month deployment to U.S. Central Command's area of operations. That area encompasses the Middle East area around the Arabian Peninsula.

The three-ship force is headed by the amphibious assault ship USS Kearsarge, which was most recently in the Persian Gulf.

A defense official says Kearsarge is in the Arabian Sea and is not expected to go to the Red Sea. The other ship in the task force is the USS Carter Hall, which is currently off the Seychelles in the Indian Ocean.