BAGHDAD, Iraq (CNN) -- A roadside bomb struck a U.S. military patrol in the northern Iraqi city of Mosul on Monday, killing five U.S. soldiers, the U.S. military said.

The military recently described Mosul as the only major Iraqi city that has a considerable presence of al Qaeda in Iraq fighters.

After the soldiers' vehicle was hit by the bomb, gunmen fired on the patrol from a nearby mosque, a military statement said.

Iraqi and coalition forces secured the area and returned fire on the insurgents, the statement said. Iraqi soldiers entered the mosque, but the gunmen had fled.

"The insurgents are willing to desecrate a place of worship by using it to attack soldiers to further their agenda," said Maj. Margaret Kageleiry, a Task Force Iron spokeswoman.

Task Force Iron is participating in Operation Iron Harvest, an offensive to root out insurgents in the northern Iraqi provinces of Nineveh, Diyala, Tameem and Salaheddin. Iraqi forces are also taking part in the operation.

Iraq's Defense Ministry announced Sunday a major movement of Iraqi forces to Mosul, Nineveh's provincial capital, as a prelude to a planned offensive intended to clear the area of Islamic fighters loyal to al Qaeda in Iraq.

The Iraqi forces include troops, special forces, tanks and Iraqi Air Force support, Defense Ministry spokesman Mohammed al-Askari told the state-run television network al-Iraqia.

Iraqi police and the army will play the lead role and will be supported by multi-national forces, he said.

A security official in the city told CNN that reinforcements from Baghdad would start arriving on Sunday and more will come over the coming two weeks.

Al-Askari would not discuss specifics.

Last week, Iraqi Prime Minister Nuri al-Maliki announced he was deploying Iraqi troops to Mosul for a "decisive" confrontation with al Qaeda in Iraq militants.

The announcement followed a massive bomb attack Wednesday in the city that killed 60 people, most of them children, women and the elderly, according to the latest figures from the Iraqi Red Cross.

"What we are planning in Nineveh will, God willing, be decisive," al-Maliki said Friday. "This heinous crime committed against our people and sons in Nineveh hurt us, but also gave us a push to expedite the activation of the operations command."

Earlier Monday, a roadside bomb struck a minibus and killed at least three people in eastern Baghdad, an Interior Ministry official told CNN.

The bomb exploded near a bus carrying a coffin in the New Baghdad district, the official said. Five other people were wounded.

Elsewhere in the capital, a fire broke out Monday morning at Iraq's Central Bank and spread to three floors of the five-story structure, the ministry said. No one was hurt.

A bank employee told CNN that employees were not allowed into the building Monday morning. Authorities have not yet determined the cause of the fire.

Iran's state-run news agency said Monday Iranian President Mahmoud Ahmadinejad will visit Iraq by the end of March.

His visit would be the first trip by an Iranian president to Iraq since the nations fought an eight-year war that killed an estimated 1 million people in the 1980s.

Ahmadinejad will go on his trip by the end of the Iranian year, which ends March 20, the country's Foreign Minister Manouchehr Mottaki told reporters.

The Iranian president will also visit a number of European countries, Mottaki said. The dates of those visits will be announced prior to the trips, the news agency quoted Mottaki as saying.

Officials in Iraq announced Ahmadinejad's landmark trip last week, but the two sides had not settled on a date at that point.

The Iranian president received the invitation when his Iraqi counterpart, Jalal Talabani, went to Tehran on an official trip, officials said.

Relations between the countries have improved since the 2003 ouster of Saddam Hussein's Sunni-led regime in Iraq.

The Bush administration accuses Iran of funding insurgents in Iraq, but both countries have long had close links.

The visit comes at a time when the United States is pushing for fresh sanctions against Iran over its nuclear program. E-mail to a friend

CNN's Jomana Karadsheh contributed to this report.

All About Iraq • Al Qaeda in Iraq • Iran