By Barbara Starr

The first of 500 Marines have begun deploying to Spain as part of a new rapid reaction force to respond to threats against U.S. citizens, government personnel or installations in Africa.

The new task force is based at Moron Air Base in southern Spain, which provides quick access especially to northern Africa, where security concerns have grown since the September 2012 attack on a U.S. government facility in Benghazi, Libya, a Pentagon official told CNN.

Deployment began Wednesday

When fully operational, the unit will be required to be airborne within six hours of receiving orders, providing the type of rapid response that the Pentagon says was not possible during the Benghazi attack. Ambassador Chris Stevens and three other Americans died during the assault at the U.S. mission and CIA annex.

The Marine unit will have the job of providing protection for embassies and diplomatic compounds under attack or receiving threats; protecting U.S. citizens; rescuing downed pilots; and assisting other elements of the U.S. military in the event of a need to evacuate American citizens, the official said. He declined to be identified because much of the group's work has not yet been publicly discussed by the Marine Corps.

Spain provided final approval for the unit's presence Friday. The full 500-strong team, which is to be in place within 30 days, will include 225 Marines equipped for ground combat along with intelligence and communications specialists, plus another 225 personnel to man and maintain the six V-22 Osprey aircraft and two C-130 refueling aircraft that make up the aviation component of the unit.

The refueling aircraft will allow the Osprey to fly greater distances without landing.

The unit is equipped to go into areas under combat conditions, and can be deployed without the permission of a local government if ordered to do so, the official said. The Marines will be equipped with machines guns, mortars and grenade launchers. Having specific aircraft assigned to the team at all times is seen within the Marine Corps as a key assurance that they can get airborne in the time required.

As part of the Marine Corps' efforts to beef up embassy security in particular, it also is adding 1,000 Marines to the embassy guard force, nearly doubling the size of the effort by increasing the size of individual embassy teams in high-threat areas, and establishing a special team of 100 Marines based in the United States that could quickly fly to an area to back up embassy guards if an embassy is under threat.