BAGHDAD, Iraq -- Thirteen U.S. soldiers were killed when a helicopter was reportedly shot down, and at least six more were killed in insurgent attacks across Iraq yesterday, in the deadliest day for the American military here in nearly two years.
The U.S. military also reported the deaths of two more troops the previous day.
The surge in fatalities just days before President Bush's State of the Union address is likely to inject renewed urgency into the debate over his Iraq policy.
The deaths come as Pentagon planners and White House officials push forward with a plan to increase the number of U.S. soldiers in Iraq by 21,500. Bush and other supporters of the plan say it is an essential move to give the Iraqi government breathing space to crack down on violent groups and heal political divisions.
Opponents, including Democratic Party leaders in Congress and some skeptical Republicans, consider it a risky escalation that could bolster anti-American sentiment in Iraq and across the Middle East, and lead to more U.S. casualties. More than 3,000 U.S. troops have been killed and 22,000 wounded in Iraq since the American-led invasion almost four years ago.
Yesterday's deadliest episode was the crash of a Blackhawk helicopter northeast of Baghdad, which killed all 13 U.S. soldiers aboard.
South of the capital in the Shiite city of Karbala, gunmen with grenades, mortars and assault rifles swarmed over a provincial security building manned by U.S. and Iraqi forces, the military said. At least five U.S. soldiers were killed and three wounded while repelling the attack.
Four more U.S. troops and 44 Iraqis were also reported killed or found dead yesterday in politically motivated violence as Iraqi and American forces stepped up an effort to target Shiite militiamen and Sunni insurgents.
U.S. military officials said the exact cause of yesterday's crash has yet to be determined, but Iraqi sources claimed it was shot down. A witness said he saw ground fire bring down the aircraft, and an insurgent group claimed responsibility for the attack in an Internet posting that could not be authenticated.
Iraqi officials and witnesses said the crash took place near the town of Buhruz in the region of Tarefiya, a rural Sunni enclave of canals and wheat fields about six miles south of Baqouba, the capital of Diyala province. The area is known as an insurgent stronghold. A recent joint U.S. and Iraqi military offensive focused on Diyala province.
A message posted to the Web by the Mujahedeen Army, an insurgent group that operates out of Baghdad and Diyala provinces, claimed responsibility for the attack.
"The helicopter was downed by anti-aircraft that belongs to the Mujahedeen Army in Buhruz," said the statement, posted to a Web site where insurgent claims frequently appear.
An Iraqi witness who spoke on the condition of anonymity said the helicopter was brought down by ground fire.
"I'm not sure if it was a rocket or other projectile," said the man, a farmer. "After the helicopter was fired upon, it was obvious that it was losing control. Then it crashed with an explosion, and the smoke started." The farmer said he and others dared not approach the wreckage to look for survivors, fearing that U.S. forces arriving on the scene might fire at them.
The U.S. military could not confirm the account. Lt. Col. Josslyn Aberle, a spokeswoman for the U.S. military in Baghdad, said that the crash took place northeast of Baghdad about 3 p.m.
"All passengers and crew were military service members," she wrote in response to an e-mail query, adding that more information was expected today. The military withheld names of the victims pending notification of family members.
An Iraqi official who spoke on condition of anonymity said U.S. forces had cordoned off a vast area of farmland and sheep pasture.
Yesterday's crash was the first since a U.S. Marine CH-53 transport chopper went down in Anbar province Dec. 11. Insurgents last shot down a helicopter May 14 near the village of Yusufiya, south of the capital.
The deadliest day for American service members in Iraq was Jan. 26, 2005, when 37 U.S. troops were killed, 31 of them in the accidental crash of a Chinook helicopter in Anbar province.
The Karbala firefight erupted as U.S. and Iraqi officials planned security for the Ashura festival, an annual Shiite pilgrimage that begins today. Karbala has come under the sway of Shiite militiamen loyal to radical cleric Muqtada al-Sadr, but it is also adjacent to Sunni Arab areas. A statement released by the military did not clarify whether the attackers were suspected Sunni or Shiite gunmen.
Four other Americans were reported killed in separate incidents.
One soldier died in northern Baghdad and another in northern Iraq yesterday when their convoys were struck by roadside bombs, and the U.S. military reported that two soldiers had died the previous day.