Two U.S. helicopters crashed Monday in northern Iraq, killing four American troops, the U.S. military said, in the deadliest single loss of life for U.S. forces in more than four months.

The military said the crash "does not appear to be by enemy action."

But the latest American deaths underscored the noncombat dangers that face the U.S. military along with continued attacks as the United States begins to draw down its forces.

On Monday, Prime Minister Nouri al-Maliki said he expects the United States to withdraw its troops faster than the three-year timeline laid down in a U.S.-Iraq security agreement that took effect Jan. 1.

President Barack Obama campaigned on a promise to remove all combat troops within 16 months and has asked the Pentagon to plan for "a responsible military drawdown from Iraq."

At a political rally Monday, al-Maliki said Iraqi forces must be bolstered with that in mind.

He said he expects the dates for the withdrawals to be brought forward ... compared with the dates set down in the agreement."

Monday's crash was the deadliest single incident for U.S. troops since Sept. 18, when seven American soldiers were killed in a helicopter crash in the southern desert west of Basra.

No precise location was given for the 2:15 a.m. crash, but a military spokesman said it occurred in Tamim province, which includes the oil-rich disputed city of Kirkuk.

Iraqi officials said the crash site was located about 20 miles west of Kirkuk, which is about 180 miles north of Baghdad. They spoke on condition of anonymity because they were not supposed to release the information.

Maj. Derrick Cheng, a spokesman for U.S. forces in northern Iraq, said all the dead were Americans. He declined to give more details.

Despite the latest crash, the number of Americans killed in Iraq has dropped significantly with an overall decline in violence.

The U.S. military relies heavily on helicopters and other aircraft to ferry troops, dignitaries and supplies to avoid the threat of ambushes and roadside bombs in Iraq.

At least 70 U.S. helicopters have gone down since the war started in March 2003, according to military figures. Of those, 36 were confirmed to have been shot down.

Most recently, a helicopter made a hard landing on Nov. 15 after hitting wires in the northern city of Mosul, killing two American soldiers.

A Soviet-made civilian cargo plane also crashed in November after reporting a malfunction west of Baghdad, leaving the seven crew members dead.

The January 2005 crash of a U.S. Marine CH-53 Sea Stallion helicopter in western Iraq claimed 31 lives — the biggest single U.S. loss of life in the Iraq war. Investigators determined the crash was not due to hostile fire.

Iraqi electoral officials, meanwhile, prepared for Saturday's provincial elections — the first nationwide vote in more than three years.

A spokesman for Iraq's Independent High Electoral Commission, Qassim al-Aboudi, said the panel had punished more than 69 parties or coalitions for 180 campaign violations ranging from putting posters outside allocated locations and defaming rivals.

He expressed concern that that was only a preview of conflicts and claims of fraud likely to emerge after the vote: "I do not expect that the losers in the elections will congratulate the winners."