Buffeted by continuing violence and the approach of a Shiite Muslim holiday, U.S. military authorities decided to reinforce troop strength in Iraq, moving hundreds of soldiers to the Baghdad area from a base in Kuwait.

Relocating an Army battalion of 700 to 800 soldiers is part of a broader plan, dubbed "Scales of Justice," that includes the repositioning of several thousand U.S. and Iraqi security forces, officials said Wednesday. They said the moves, which include two other Army battalions, come in anticipation of potential sectarian violence related to a Shiite pilgrimage this month marking the holiday.

The only unit added from outside of Iraq is the battalion from Kuwait, which is part of the 1st Armored Division.

In a brief written announcement, the U.S. military headquarters in Baghdad did not mention the number of soldiers in the battalion that moved from Kuwait, but officers at the Pentagon said it was between 700 and 800 and included mechanized infantry with Bradley fighting vehicles as well as combat engineers.

The officials who provided details beyond what was announced in Baghdad did so on condition they not be identified.

Gen. George Casey, the top U.S. commander in Iraq, was quoted in a news release from Baghdad as saying he had discussed the plan with Iraqi Prime Minister Ibrahim al-Jaafari, "and we found it prudent to provide this additional support."

"We called forces forward to provide support to the ISF (Iraqi security forces) for a safe observance of the Arba'een religious holiday and the formation of the new Iraqi government," Casey added.

Casey said the battalion would return to Kuwait "after its mission is completed," but did not elaborate.

The general did not say whether additional troop increases might be needed this spring. Just last week, Defense Secretary Donald H. Rumsfeld said that while U.S. forces were prepared to support the Iraqis during any escalation of sectarian violence, the plan was to rely mainly on Iraq's own security forces in the event of all-out civil war.

The "Scales of Justice" plan, which focuses on averting or responding to violence connected to the pilgrimage and the political wrangling over formation of a new government, includes two Iraqi army battalions and three Iraqi national police battalions, in addition to the three U.S. Army battalions. No total number of personnel associated with this plan was provided in the Baghdad announcement, but it appeared to exceed 4,000.

The holiday pilgrimages are to holy sites in Najaf and Karbala, predominantly Shiite areas where the potential for sectarian violence would be of great concern. Increased attacks marked the celebration during 2004 and 2005.

Monday marks the end of the 40-day mourning period after the death of Imam Hussein in 680 AD. He was the grandson of the Prophet Muhammad and was killed in Karbala in present day Iraq, now the site of large Shiite pilgrimages to mark the date.

The military moves come amid a spike in sectarian violence and expectations that it likely will remain a problem as fractious Iraqi political leaders attempt to form a new government.

The decision to add the armored unit from Kuwait, perhaps for as little as 30 days, is in contrast to the Bush administration's hopes of substantially drawing down the U.S. military presence in Iraq this year. There are currently about 133,000 troops there.

It also comes amid administration efforts to persuade the American public that the war effort is succeeding. Opinion polls show faltering public support for the war.

At the White House, presidential spokesman Scott McClellan said he did not know of the decision to add U.S. troops in Iraq. He said force levels are adjusted based on recommendations from commanders in Iraq.

"The situation in Iraq remains a serious one and a tense one, and it's important that Iraqi leaders continue to move forward on forming a government of national unity that represents all Iraqis," McClellan said. "Those discussions are ongoing. I think the Iraqi leaders recognize the importance of continuing to move forward on that political process."

Bryan Whitman, a senior Pentagon spokesman, noted that Rumsfeld had said on Tuesday that U.S. commanders could decide they need to temporarily boost troop levels because of the pilgrimage.

"General Casey may decide he wants to bulk up slightly for the pilgrimage," Rumsfeld said at the time. "And we're continuing to pull troops down. And we're continuing to shift our weight, as we've said, between the combat patrol aspects of it, over to the training and the equipping and providing the enablers."

Hundreds of people have been killed since the Feb. 22 bombing of a Shiite mosque in Samarra, creating concern that the country may be tipping toward civil war.

The mechanized infantry battalion that is being sent to Iraq is one of three from the 2nd Brigade, 1st Armored Division that originally were scheduled to deploy to Iraq but were instead held in Kuwait as a standby force in the event Casey decided he needed extra troops. It's not clear how long the battalion will remain in Iraq, the officers said.