BAGHDAD, Iraq (CNN) -- Two suicide vehicle bombers struck a U.S.-Iraqi military outpost in Taji on Wednesday night, the U.S. military said in a statement.
U.S. Black Hawk helicopters fly over Baghdad in June. A Black Hawk chopper crashed Wednesday in Iraq.
The attack killed four Iraqi soldiers, the military said, and wounded 11 U.S. soldiers and four Iraqi soldiers.
The incident occurred at 8:45 p.m., according to an Iraqi Interior Ministry official.
Eight Iraqis suspected of having information concerning the attack have been detained, the U.S. military said.
Taji is 14 kilometers, or more than 8 miles, north of the capital, but still in Baghdad province.
Police in Taji said the base is in the Haw al-Basha area. Police said that when they responded, U.S. troops fired on them and would not allow them near the base.
Earlier Wednesday, 14 U.S. soldiers died when their helicopter crashed in northern Iraq, the U.S. military said.
Separately, at least 37 people were killed and 81 wounded when a suicide car bomb detonated outside a police building in the Iraqi town of Baiji, north of Baghdad, in Salaheddin province, police said.
Also Wednesday, a U.S. soldier was killed and three others wounded in combat west of Baghdad, the military said.
The helicopter crash occurred near Kirkuk, according to a U.S. military intelligence source. Watch the initial report of the copter downing »
"Two UH-60 Black Hawk helicopters were on a night operation when one of the aircraft crashed," the military said.
"Initial indications are that the aircraft experienced a mechanical malfunction. There were no indications of hostile fire."
The military has launched an investigation into the crash, the deadliest since January 2005, when a helicopter went down in western Iraq and killed 31 Marines. Since the start of the war, 3,715 U.S. troops have died in Iraq; seven civilian contractors also have been killed.
There have been a string of helicopter downings in Iraq this year. In January, 12 U.S. soldiers were killed when a U.S. helicopter went down northeast of Baghdad.
The Brookings Institution's Iraq Index, a regularly updated compilation of facts about the war, said in its latest update Monday before this crash that 67 American military helicopters have gone down since May 2003 and that enemy fire had downed at least 36.
Meanwhile, police in Baiji said an explosives-packed truck drove into the police directorate's compound in the center of town and detonated.
A number of homes in the compound were destroyed. The police building was badly damaged, and 15 vehicles were destroyed.
On the political front, Iraqi Prime Minister Nuri al-Maliki responded to U.S. criticism of his government, calling such comments irresponsible and saying they "overstep the bounds of diplomatic and political courtesy."
President Bush and the U.S. ambassador to Iraq, Ryan Crocker, on Tuesday expressed frustration with an ineffective Iraqi political process dominated by constant governmental squabbling.
Democratic Sen. Carl Levin of Michigan, chairman of the Senate Armed Services Committee, on Monday called on Iraq's parliament to turn al-Maliki's "nonfunctioning" government out of office when it returns in two weeks. He said al-Maliki's government was "too beholden to religious and sectarian leaders" to reach a political settlement that would end the country's sectarian and insurgent violence.
"Everyone knows that the Iraqi government is one elected by the Iraqi people, and no one puts timetables or restrictions other than the Iraqi people who elected the government," al-Maliki said Wednesday during a visit to Syria's capital, Damascus. Government spokesman Ali Dabbagh said al-Maliki was specifically referring to Levin's comments.
White House spokesman Gordon Johndroe on Wednesday said media reports had overblown differences between the Bush administration and al-Maliki. Johndroe said al-Maliki is Iraq's elected prime minister, and the Iraqi government is working to achieve political reconciliation.
CNN's Jomana Karadsheh and Raja Razek contributed to this report.