At least 33 people have been killed and dozens injured in a wave of bombings and shootings across Baghdad.

Officials said the attacks appeared to be targeting police officers.

Nine people were killed in the worst attack, in the central Karrada district, which is mainly Shia. The blast, near a police checkpoint, shook buildings and damaged shops.

No group has yet said it was behind the violence. Attacks in Iraq have risen since US troops withdrew in December.

In other attacks on Thursday, six people were killed by a car bomb in al-Kadhimiya, north of Baghdad, while gunmen in the Sarafiya district of the capital also killed six at a police checkpoint.

Last week, at least 18 people were killed in a suicide attack near the Iraqi police academy in the capital.

There are fears the death toll from Thursday's violence could rise.

There are also reports of bombings in the provinces of Salahuddin, Diyala and Kirkuk.

The capital of Salahuddin province is Tikrit, the home town of former leader Saddam Hussein, who was executed in 2006.

Shia targets have come under increasing attack since the government of Shia Prime Minister Nouri al-Maliki moved against senior members of the predominantly Sunni Iraqiya political bloc.