Updated

The Pentagon (search) has ordered 1,500 additional troops to Iraq to provide security in advance of two upcoming votes, the military announced Wednesday.

Two infantry battalions from the 82nd Airborne Division (search) will deploy to Iraq before the scheduled Oct. 15 referendum on the proposed constitution, and remain through the December national elections, officials said.

They will join the 138,000 U.S. troops already there. The battalions are expected to remain in Iraq for 120 days.

The military anticipates an increase in violence in Iraq in advance of the elections, with insurgents opposed to the U.S.-backed government trying to disrupt the process.

The Pentagon has temporarily increased the size of the force in Iraq twice before political milestones -- the June 2004 transfer of sovereignty and the January elections. Lt. Col. Barry Venable, a Pentagon spokesman, said those deployments helped limit the effectiveness of the insurgent campaign.

"This deployment is in support of continued progress," he said. "We are reinforcing success."

The troops are being sent at the request of Gen. George Casey (search), commander of the multinational forces in Iraq.

The Pentagon has already sent additional troops to Afghanistan to bolster security for September elections there.

The 82nd Airborne Division is based at Fort Bragg (search), N.C. It was not immediately clear when the troops would depart.

Another battalion from the 82nd Airborne is deploying to Iraq to assist with detention operations, the military recently announced.