Jan. 22 (Bloomberg) -- At least 25 U.S. military personnel were killed in Iraq on Jan. 20 in one of the worst days for American forces in the 2003 invasion.

Twelve U.S. soldiers were killed when the Blackhawk helicopter in which they were riding crashed northeast of Baghdad two days ago, the U.S. military said in a statement yesterday. Earlier reports said 13 passengers and crew members were killed. Five soldiers were killed when militiamen attacked a security coordination center in Karbala and four soldiers and a Marine died in western al-Anbar province, the military said. Three other soldiers were killed in separate attacks across the country.

The losses are the heaviest suffered by the military in a single day since Jan. 26, 2005, when 30 U.S. Marines and a sailor were killed in a helicopter crash caused by a sandstorm.

U.S. President George W. Bush is sending an additional 21,500 American forces to Iraq in an attempt to quell violence against coalition forces and the country's warring sectarian factions. U.S. Democrats are planning House and Senate votes on nonbinding resolutions opposing the strategy and are considering trying to block the deployment by withholding funds.

The cause of the helicopter crash is under investigation, the military said. There were no survivors.

Marines Killed

Two Marines were killed in separate incidents yesterday in al-Anbar province ``from wounds sustained due to enemy action,'' the U.S. military said in an e-mailed statement late yesterday. At least 45 U.S. service personnel have been killed since the start of 2007, according to military statements and Department of Defense figures.

The 2nd Brigade of the 82nd Airborne Infantry Division comprising about 3,200 soldiers arrived in Baghdad on Jan. 20, one of the first units deployed to increase the numbers of forces by 21,500 personnel in Baghdad and al-Anbar. The Iraqi capital is the center of Iraq's civil conflict between warring religious, ethnic and territorial factions. Baghdad and neighboring al-Anbar are the most dangerous areas of operation for coalition forces.

More than two-thirds of Americans oppose the strategy, a Newsweek magazine poll found.

Sixty-eight percent of those responding said they opposed Bush's planned troop ``surge'' in Iraq, including 45 percent who said they were strongly opposed.

Twenty-six percent favored the approach, announced by Bush in a televised address to the nation Jan. 10.

The poll, released Jan. 20 and to be published in the Jan. 29 issue of Newsweek, has a margin of error of plus or minus four percentage points. It is based on interviews of 1,003 adults on Jan. 17 and 18.

A total of 2,434 U.S. service personnel had been killed in action since the March 2003 invasion of Iraq, as of Jan. 19, according to figures posted on the Department of Defense Web site. The number of deaths including those who died from other causes, such as accidents and illnesses, was 3,019.

To contact the reporter on this story: Ed Johnson in Sydney at ejohnson28@bloomberg.net.

Last Updated: January 22, 2007 04:13 EST