A homicide car bomber struck police in the northern city of Mosul on Monday, killing at least seven people and wounding 25.

The attacker detonated an explosives-laden car after approaching the checkpoint at the provincial police headquarters in the city's main commercial district, a police officer said, speaking on condition of anonymity because he was not authorize to release the information. He said three policemen and four civilians were killed.

The U.S. military has called Mosul the last urban stronghold of Al Qaeda in Iraq. U.S. and Iraqi forces have been conducting sweeping operations in recent weeks to clear the area.

American troops killed two suspects, captured 31 others and destroyed bomb-making materials over the past two days in raids targeting Al Qaeda in Iraq in central and northern swaths of the country, the military said Monday.

The two deaths occurred when American soldiers returned fire and called in air support after coming under machine-gun fire from "multiple enemy positions," according to a U.S. military statement. The battle took place early Monday in a remote area northwest of Tikrit about 100 miles north of the Iraqi capital, it said.

U.S. troops also found a car filled with bomb-making materials and suicide vest components, and tunnels leading to a sleeping area and place where weapons were stored, the statement said.

Among those detained were a "leader of terrorist finances" in Mosul, an expert in car bomb tactics and others with direct links to senior Al Qaeda in Iraq figures, it said.

Meanwhile, Iraqi security forces arrested a top suspect in the Soldiers of Heaven cult, whose members seek to invoke chaos as a means of inspiring the return of the "Hidden Imam" — a descendant of the prophet Muhammad who disappeared as a child in the ninth century. Shiites believe he will return one day to bring justice to the world.

One of the cult's leaders, Munadhal Abdul Karim, was captured Monday at a coffee shop in central Basra, said Maj. Gen. Mohammed Jawad Huwaidi, commander of Basra military operations.

Soldiers of Heaven followers are said to have a number tattooed in blue ink on the back of their necks, confirming membership.

Huwaidi said Abdul Karim was responsible for several killings, but he did not give details.

In recent months, Iraqi forces have battled Shiite militants in Basra, Iraq's second-largest city, seeking to extend their control over the southern oil hub after British troops pulled back from the area last year.

In a separate statement issued Monday, the U.S. military said it captured a criminal suspected of manufacturing and planting roadside bombs northwest of Baghdad.

Soldiers with the 25th Infantry Division arrested the suspect Saturday in Tarmiyah, 30 miles north of Baghdad, the statement said.

He was allegedly responsible for the bombing deaths of several Iraqi soldiers and civilians, and also connected to the bombing of a bridge north of the capital that killed several Iraqis last year, it said.

Also Monday, the state-run newspaper Al-Sabah reported that Prime Minister Nouri al-Maliki would travel to Iran next week. It quoted Iraqi government spokesman Ali al-Dabbagh as saying al-Maliki would head a delegation leaving for Tehran on Saturday.

An official in al-Maliki's office confirmed the report and added that the prime minister would also travel to Jordan. He gave no further details and spoke on condition of anonymity because he was not authorized to release al-Maliki's travel schedule.

Iranian state television also reported the upcoming visit.