BAGHDAD, Iraq (CNN) -- Five U.S. soldiers were killed Friday in a suicide bombing in the northern Iraqi city of Mosul -- the single deadliest attack on U.S. troops in more than a year, the U.S. military said.

A suicide truck bomber breached the outer security barrier of Iraqi National Police headquarters in southern Mosul, and detonated his explosives, killing eight people and wounding 60 others, an Iraqi Interior Ministry official said. A U.S. soldier was also among the wounded, the U.S. military said.

The ministry said those killed include five Americans, two Iraqi policemen and an Iraqi soldier. At least two individuals suspected of being involved in the attack were detained, the U.S. military said.

It is the deadliest attack on U.S. forces since March 10, 2008, when five U.S. soldiers were killed in a suicide attack in Baghdad.

Despite a number of military operations in this volatile city during the past year, Mosul remains one of the most violent places in Iraq. Last year the U.S. military said Mosul was the last urban stronghold of al Qaeda in Iraq.

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Mosul is the provincial capital of Nineveh and is about 260 miles, or 420 kilometers, north of Baghdad. Watch a suicide bomb attack kills 5 U.S. soldiers »

U.S. and Iraqi military forces plan to pull out of Mosul to allow Iraqi police to control security in the city. But police are not quite ready yet, according to an Iraqi general.

"We need to bring the police to the required level. The deadline is the end of July, and it's not enough time to prepare the police," said Gen. Hassan Karim, commander of Nineveh operations for the Iraqi army. "(That) means we'll need U.S. forces to stay in Mosul."

CNN's Nic Robertson contributed to this report

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