A homicide car bomber struck a busy commercial district in central Baghdad on Monday, killing at least 21 people and damaging a Sunni shrine, police and hospital officials said.

The bomb went off at 2 p.m. in the Sinak commercial district on the east side of the Tigris River near the Abdul-Qadir al-Gailani mosque.

AP Television News video showed dozens of astonished people at the scene of the Sinak explosion as they walked around charred cars and debris that littered the scene. Firefighters in yellow helmets struggled to extinguish the fire as ambulances rushed to evacuate the wounded.

Ghaith Karim, a 38-year-old Shiite cloth merchant, was heading to the bus station near Sinak when he saw a fireball and heard the loud blast: "It was tremendous. I felt the ground was shaking."

The cleric in charge of the mosque, Mahmoud al-Issawi, said the blast also damaged the building's dome, while the footage showed damage to its minaret.

"The enemies of Iraq are the only one who get benefit out of that bombing. These enemies have targeted our homeland, religion and our brotherhood," al-Issawi told Iraqiya TV.

Also in central Baghdad, a battle raged after insurgents hijacked two buses and kidnapped at least 15 passengers, police said. At least three policemen were killed.

The small buses where traveling through the Fadhil neighborhood, a Sunni enclave in central Baghdad, when they were waylaid by gunmen in three cars.

The insurgents abducted at least 15 passengers and took them to an abandoned government building neaby, a police officer said on condition of anonymity because he was not authorized to talk to reporters.

Security forces arrived within 30 minutes and came under attack from militants firing at them from nearby alleys. According to Iraqi police, at least two U.S. helicopters hovered overhead and Americans took up positions near the fighting, but were not directly involved.

Nine militants were arrested.

Separately, police said that a roadside bomb killed two people and injured nine when it detonated under a parked car in the central Baghdad district of Bab al-Muadham. Another two people were killed and six were wounded after two mortar rounds slammed into a street in Karrada, a Shiite-dominated neighborhood in downtown Baghdad, police said.