A female suicide bomber wearing a black abaya detonated her explosives belt in a crowd of about 200 police recruits northeast of Baghdad on Tuesday, killing at least 14 people, police and hospital officials said.
The woman walked into the crowd at the main gate of the Muqdadiyah police station, according to a police officer at the scene who spoke on condition of anonymity because he was not authorized to speak to the media.
At least 14 people were killed and 20 injured, said an official at Muqdadiyah General Hospital, also on the same condition of anonymity. The death toll was expected to rise.
The police recruits had gathered at the station to eagerly await word about whether they were accepted into the police force there, the officer said.
Muqdadiyah, a mostly Sunni Muslim city, lies about 60 miles northeast of Baghdad.
Also Tuesday, the U.S. military announced the deaths of four U.S. soldiers three killed by a roadside bomb in Baghdad and another killed in combat in western Anbar province.
The three were killed Monday by a roadside bomb and a secondary explosion while on patrol in a southeastern section of the Iraqi capital, the U.S. military said in a statement.
The unit had been conducting raids against militants in the area, and had recently captured five suspects, it said.
Another U.S. soldier was killed the same day while conducting combat operations in Iraq's western Anbar province, another statement said.
The soldiers' names were withheld pending family notification.
At least 3,285 members of the U.S. military have died since the beginning of the Iraq war in March 2003, according to an Associated Press count. The figure includes seven military civilians.
Repeated artillery fire rang out across Baghdad at midday Tuesday, but the target was unclear. U.S. forces were engaged in fierce fighting with gunmen in two Sunni-dominated neighborhoods of the capital, Fadhil and Sheik Omar, police and witnesses said.
An American helicopter involved in the battle came under ground fire but was not shot down, a senior U.S. military official said. He spoke on condition of anonymity because U.S. officials were still investigating the incident.
Four civilians were injured in the clashes, police and a hospital officials said.
Prime Minister Nouri al-Maliki, on a four-day trip to Japan, said Tuesday that there was no need to set a timetable for the withdrawal of U.S. troops from his country.
"We see no need for a withdrawal timetable. We are working as fast as we can," al-Maliki told reporters. "To demand the departure of the troops is a democratic right and a right we respect. What governs the departure at the end of the day is how confident we are in the handover process."
What counts, he added, are "achievements on the ground."
His comments came a day after tens of thousands of Iraqis took to the streets of two Shiite holy cities, demanding that U.S. forces leave their country. The massive rally, called for by rebel cleric Muqtada al-Sadr, marked the fourth anniversary of the fall of Baghdad.
Al-Sadr, who remains in seclusion and did not attend, ordered up the march as a show of strength not only to Washington but to Iraq's establishment Shiite ayatollahs as well.
He issued a statement Sunday calling on his Mahdi Army militia to redouble efforts to expel American forces and for the police and army to join the struggle against "your archenemy."
Also Tuesday, the U.S. military said it captured more than 150 suspected insurgents in a nearly two-week operation north of Baghdad. Rocket-propelled grenades and launchers, automatic machine guns, sniper rifles and anti-tank mines were also seized, it said.