(Adds time of deployment, more background)

By Andrew Gray

WASHINGTON, Dec 19 (Reuters) - Defense Secretary Robert Gates has ordered a U.S. Army combat aviation brigade to Afghanistan as part of a buildup of forces to counter rising insurgent violence, officials said on Friday.

A military official said the U.S. Army brigade of about 2,800 soldiers was equipped with both attack and transport helicopters. The troops would deploy to Afghanistan in the spring, a senior defense official said.

Both officials spoke on condition of anonymity as the deployment has not yet been officially announced.

The brigade will form part of an increase of some 20,000 troops requested by U.S. Army Gen. David McKiernan, the top commander of all NATO and most U.S. forces in Afghanistan.

McKiernan has asked for the extra troops to halt a growing insurgency made up of Taliban militants and other groups, particularly in the east and south of Afghanistan.

His request includes four combat brigades of ground forces -- about 14,000 troops -- and extra support units.

One of the ground combat brigades is scheduled to deploy in January and Gates, who will continue as Pentagon chief under President-elect Barack Obama, told reporters last week he expected to provide two more by late spring.

Obama has pledged to put a renewed focus on Afghanistan, where U.S.-led forces toppled the Taliban government in late 2001 after the Sept. 11 attacks on the United States.

The United States has some 31,000 troops in Afghanistan, some of them operating independently and some operating as part of a 51,000-strong NATO-led security assistance force.

McKiernan has said his planned troop increase should not be compared to the temporary "surge" of forces in Iraq in 2007, widely credited with helping to reduce violence, because higher troop levels could be needed in Afghanistan for years.

He told reporters traveling with Gates on a visit to Afghanistan last week that Afghan forces needed to develop for three or four more years before they would become less dependent on international troops. (Editing by Eric Beech)

AlertNet news is provided by