BAGHDAD: A powerful car bomb killed at least 30 people in Iraq's main northern city of Mosul on Friday in a wave of attacks targeting Shiites that also left four dead in the capital Baghdad.

Police said a further 72 people were wounded in the Mosul suicide bombing, the latest in a spate of deadly attacks against Shiites which have stoked fears of a return to the sectarian conflict which swept the country in 2006 and 2007.

The bomb targeted a Shiite mosque used by members of the Turkmen minority in the mainly Sunni Muslim city 370 kilometres (230 miles) north of Baghdad, a police official told a foreign news agency.

There was carnage when the explosives were detonated as worshippers left the building after the main weekly prayers.

The force of the blast levelled the mosque and several adjacent buildings, and police said they were sifting through the rubble searching for casualties.

"When we arrived, there was blood everywhere and pieces of flesh all over the ground and walls," police Lieutenant Khaled Rajab said. "The mosque and several houses were flattened and we began searching through the rubble."

Friday's bombing came as a string of attacks in the capital targeted Shiites returning from the central shrine city of Karbala after a key religious ceremony, an interior ministry official said.

A roadside bomb at the entrance to the sprawling Baghdad Shiite district of Sadr City ripped through a bus, killing three pilgrims and wounding eight, the official said.

"The inside of the bus was covered in blood," trader Abu Mohammed said.

Local resident Abbas Jumaa, 27, said: "I saw women and old men... They are only pilgrims and they don't carry guns. So why would anyone attack them?"

A second bombing at the edge of Sadr City an hour later wounded another five people travelling in a minibus from Karbala.

One person was killed and five wounded in a separate roadside bombing on a minibus carrying pilgrims in the Zayune neighbourhood of central Baghdad, the official said.

Roads to and from Karbala have been crowded with pilgrims in vehicles or on foot this week as Shiites commemorate the birth of the Twelfth Imam, a disappeared ninth century Muslim leader revered as a coming messiah.

Despite the marked reduction in violence in recent months, attacks against security forces and civilians remain common in Baghdad, Mosul and the ethnically divided northern oil city of Kirkuk.

The number of violent deaths fell by a third from the June figure of 437 to 275 in July, the first month Iraqi forces have been in charge of security in urban areas since the US-led invasion of 2003.

The figure in May was 155, the lowest of any month since the invasion.

A string of six powerful bombs targeting Shiite worshippers in Baghdad last week killed 28 people and wounded 63.LINK