A car bomb exploded near a police patrol in central Baghdad on Thursday, killing at least 17 civilians and wounding 20, destroying cars and devastating a nearby building, police and witnesses said.
"A car bomb hit a police patrol, wounding several policemen," a police officer at the scene said. "There must also be civilian casualties because it is a busy area."
The explosion brought down the roof and walls of a nearby building, and passersby and rescue workers searched the ruins for survivors.
The blast set several cars ablaze, sending black smoke billowing into the air. A line of cars had been queuing at a nearby petrol station when the car bomb detonated. The station itself did not catch fire.
Twisted metal and shards of
glass littered the blast site
Twisted metal and shards of glass littered the commercial Saadun Street district as police cars rushed to the scene.
"My clinic shook and is now filled with sand and dust," said Dr Anwar Barnuti, who runs a clinic nearby.
The US military had no information on the blast, which took place about 11:30am (0830 GMT) in Nasr Square, where a statue of a former Iraqi prime minister stands.
The blast follows close on the heels of another car bomb near the culture ministry in Baghdad that killed seven people on Wednesday.
Also on Thursday, north of Baghdad a national guardsman was killed and 17 people were injured in separate attacks, including a car bombing against the governor of Kirkuk, who escaped unharmed, police said. Four of Abd al-Rahman Mustafa's bodyguards were among the wounded when the explosion ripped through his convoy as it drove through the city's northern Imam Kassim neighbourhood, police chief Turhan Yusif said.
The attack, at about 9am (0600 GMT), wounded 10 passersby, according to Dr Rida Abd Allah of the Kirkuk general hospital.
"My clinic shook and is now filled with sand
Baghdad doctor Anwar Barnuti
It is the first time that the governor of ethnically charged Kirkuk, 250km north of Baghdad, has been targeted.
In another incident on Thursday, a loud explosion rocked an oil well west of the city, sources told Aljazeera.
On a day violence surged in Iraqi towns and cities, about 30 armed men attacked a National Guard station at dawn in Baquba, 60km north-east of the Iraqi capital, Muhannad Mahmud, a guardsman, said.
One guardsman was killed and three others were injured in the incident, he said.
Iraq's fledgling security forces and all other symbols of the US-backed government are prime targets for a potent anti-US movement that has raged since the aftermath of last year's invasion.
In a separate development, a number of armed fighters have taken over control of six police centres in Mosul city, sources told Aljazeera.
The fighters confiscated the police centres' weapons and burnt some of them on Thursday. They also set fire to a number of police vehicles, the sources said.
The US forces closed five bridges
in Mosul amid escalating violence
For their part, US forces backed by armoured vehicles separated the two sides of the city by closing four of the five bridges on the Tigris river, Muhammad Zu al-Nun, an Iraqi journalist, told Aljazeera.
Later loud explosions rocked the city as US military bases in different areas in Mosul came under attack from mortar shells and Katyusha missiles.
Against this backdrop of bloody clashes, a large number of US forces and Iraqi national guards have cordoned off the neighbourhood of al-Amiriya, west of Baghdad, Aljazeera learnt.
On Thursday, US soldiers prevented citizens from leaving their homes in order to search them. Large numbers of US military vehicles have been deployed in the city.
The action came in the wake of fierce clashes on Wednesday between US forces and armed fighters.