BAGHDAD, Iraq – An American Army Black Hawk helicopter went down in northern Iraq, killing all 12 Americans believed to be aboard in the deadliest crash in nearly a year, while five American Marines died in weekend attacks, the military said yesterday.

The latest deaths followed an especially bloody week in which about 200 Iraqis and a dozen American troops were killed. Iraqi politicians, meanwhile, claimed headway in forming a stable coalition government following the December 15 elections, the final results of which may be released this week.

American military officials said the UH-60 Black Hawk crashed just before midnight Saturday about seven miles east of Tal Afar, a northern city near the Syrian border that has seen heavy fighting with insurgents.

“All [those killed] are believed to be U.S. citizens,” a military spokesman, Lieutenant Colonel Barry Johnson, said.

He did not say what caused the crash, but bad weather has wracked most of Iraq.

The Black Hawk was part of a two-helicopter team providing support for the 101st Airborne Division and was flying between bases when communications were lost, the military said. After a search, the helicopter was found about noon yesterday, the military said.

The helicopter was part of Task Force Band of Brothers and attached to the 101st Aviation Brigade, but a spokesman for the division’s 3rd Brigade, Major Tom Bryant, said the helicopter was not from Fort Campbell, Ky., and belonged to another unit.

Major Bryant could not say what unit the helicopter belonged to or whether any soldiers from the 101st were aboard. Master Sergeant Terry Webster of division public affairs could not identify what unit operated the helicopter.

In Saturday’s crash, records indicated that eight passengers and four crew members were aboard.

Three Marines were killed yesterday by small arms attacks in Fallujah, 40 miles west of Baghdad, the military said. Two other Marines were killed Saturday by roadside bombs in separate incidents, the military said.

In other violence yesterday, five people died in separate attacks in Baghdad, including a policeman killed by a suicide car bomber targeting an Interior Ministry patrol. Seven others were wounded.

Meanwhile, a French engineer abducted December 5 was dumped on a Baghdad street by his fleeing captors and recovered by American troops, who turned him turned over to the French Embassy on Sunday, according to Iraqi police and the French Foreign Ministry in Paris.

Bernard Planche, 52, was kidnapped on his way to work at a water plant. Mr. Planche worked for a non-governmental organization called AACCESS and was found Saturday night near a checkpoint in the Abu Ghraib neighborhood. His captors had demanded the withdrawal from Iraq of French troops – even though the country has none in Iraq.

The leader of Iraq’s main Sunni Arab political group said after meeting President Talabani that significant headway had been made in efforts to form a government of national unity.