A U.S. Marine, from the 24th Marine Expeditionary Unit, runs for cover near the town of Garmser in Helmand Province May 19, 2008. REUTERS/Goran Tomasevic

WASHINGTON (Reuters) - About 1,000 Marines deployed to train Afghan security forces will have their tours of duty extended by 30 days, a U.S. defense official said on Monday.

The official, who spoke on condition of anonymity, said the Pentagon has also decided to send fewer than 200 support troops to enhance the ability of Marine trainers to engage in combat with insurgents while on exercises with Afghan forces.

The extension, which has not been officially announced, follows an identical move last month for another group of Marines battling insurgents in southern Afghanistan.

Extended Marine tours come amid U.S. concern about rising violence in Afghanistan from the Taliban and other groups, including militants that U.S. military officials say are being trained and equipped at safe havens in neighboring Pakistan.

U.S. forces invaded Afghanistan in 2001 and toppled the Taliban government after the September 11 attacks.

The latest Marines to have their tours extended belong to the 27th Marine Expeditionary Unit, which deployed in April for a seven-month tour that was due to end in November. The extension will keep them in Afghanistan into December.

Last month, the Pentagon issued a one-month extension for some 2,200 Marines who deployed for combat duty in March from the 24th Marine Expeditionary Unit. That extended their stay from October to November.