Updated

The Pentagon has ordered roughly 1,250 Marines serving as trainers for the Afghan security forces to stay on the warfront about a month longer to continue a mission that military leaders say is a top priority, according to a senior military official.

In addition, Defense Secretary Robert Gates has authorized the deployment of up to 200 other troops to Afghanistan to support the Marines. That includes eight helicopter crews that could be shifted from Iraq if commanders decide.

The senior military official spoke to The Associated Press on Monday on condition of anonymity because the formal announcement has not yet been made.

The decision to extend the tour of the 2nd Battalion, 7th Marine Regiment in Afghanistan comes just a month after defense officials told the 24th Marine Expeditionary Unit that it would stay an extra month in Afghanistan.

According to the official, the decision to hold the battalion there longer is part of an effort to capitalize on the gains the Marines have made in the training mission. The extension means that the battalion would return home in late November.

Gates' decision to send the other support forces comes after weeks of discussions by top military leaders who scrambled to find needed troops. He authorized Army Lt. Gen. Martin E. Dempsey, who is temporarily in charge of U.S. Central Command, to shift up to eight helicopter units from Iraq to Afghanistan -- four Cobra attack aircraft and four MH-53 heavy lift helicopters.

The remainder of the support forces being deployed are smaller units, including engineers, route clearance troops and explosive ordnance disposal teams. It was not clear Monday whether those support forces also would return home in late November, or if they would stay longer in Afghanistan.

Late last week Gates hinted at the moves, saying the Pentagon was "looking at" sending a couple hundred troops at the most to Afghanistan soon.

The Pentagon announced in January that the Marine Expeditionary Unit, which is based at Camp Lejeune, N.C., was being ordered to Afghanistan, largely because efforts to press other NATO nations to increase their troop levels at the time had failed. The MEU has been fighting Taliban militants in the volatile south.

At the same time, the 2nd Battalion, 7th Marine Regiment, which is based at Twentynine Palms, Calif., was ordered to deploy also.

Gates has said he would not replace the Marines with other U.S. troops when they left later this year. But commanders have said they need three more combat brigades -- or as many as 10,000 troops -- to bolster the fight in Afghanistan. And U.S. officials have indicated they would like to send extra brigades there next year.

Military leaders, however, have made it clear they need to free units from Iraq deployments in order to send more troops to Afghanistan. As security in Iraq continues to improve, officials have suggested that units initially headed for Iraq late this year or early next year could be sent to Afghanistan instead.