The first bombs began shortly after sunrise, and were followed by reports of mortar shells being fired at police posts. Gun battles were still continuing six hours later, police officials said.

Four policemen were killed and eight were injured in a suicide car bombing in the Al-Nour quarter in eastern Mosul, said General Within al-Hamdani, the provincial police commander.

He said this provoked gun battles which moved from street to street through five neighbourhoods in Mosul, 225 miles northwest of Baghdad. Throughout the course of the battles, two other cars blew up but caused no casualties.

Further south in Nineveh, in the town of Al-Hadrah, a suicide car bomber drove into a football field, killing ten people, including three Iraqi policemen and seven civilians who were among the players, a police source said.

The car bomber, who ploughed into a police post protecting the football match, also wounded 15 people, including nine policemen who were patrolling the area.

A roadside bomb killed a pregnant Iraqi woman and her husband in Huweidar in the early hours of the morning as they raced to hospital to deliver her child. The couple had been taking a taxi from the village at 2am towards the maternity hospital in Diyala, north of Baghdad.

The fighting comes a day after some of the most senior American and British officials responsible for policy in Iraq warned that the country was sliding into civil war.

General Wathiq al-Hamdani said the Mosul clashes were inspired by Osama bin Laden.

"These are members of al-Qaeda that we clashed with. We killed large numbers of them and we burned their trucks and vehicles," he told the state television. "We are in full control of the situation. The people of Mosul were very helpful."

A curfew has now been imposed throughout Mosul and Iraqi forces took control of the streets once the fighting subsided.

Mosul authorities have ordered everyone off the streets until Saturday and closed the city’s bridges across the Tigris river.

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