Four bombs in mainly Shi'ite Muslim areas in Baghdad killed at least 29 people and wounded dozens of others on Thursday, police and hospital sources said, as fears of renewed sectarian strife in Iraq increase.

Shi'ite Prime Minister Nuri al-Maliki sparked the worst political crisis in a year on December 19 when he sought the removal of two senior Sunni politicians just as U.S. troops withdrew from Iraq. Bombings on December 22 in the predominately Shi'ite parts of Iraq's capital killed 72.

On Thursday, in Baghdad's northeastern impoverished Sadr City slum, a bomb planted on a parked motorcycle and another roadside explosive killed at least 10 people and wounded 37 others, police and hospital sources said.

Police said they found and defused two other bombs.

There was a group of day labourers gathered, waiting to be hired for work. Someone brought his small motorcycle and parked it nearby. A few minutes later it blew up, killed some people, wounded others and burned some cars, said a police officer at the scene, declining to be named.

A Reuters reporter said there were blood stains around the site of the motorcycle bomb attack and that tarmac on the road had been ripped up by the explosion. Building tools and shoes were scattered across the site.

Reuters TV video from Sadr City hospital showed a crowded emergency room with many injured people and their relatives. One man sat on the floor, hugging his younger brother, as they cried for their sister who was killed in one of the blasts.

The second set of explosions, two car bombs, occurred in Baghdad's northwestern Kadhimiya district and killed at least 15 people and wounded 32, police and hospital sources said.

People started to flee from the explosions and others ran towards them (to look for relatives). The scene was like a play, with people crying and screaming and falling, Ahmed Maati, a policeman in Kadhimiya, told Reuters.

SECTARIAN TENSIONS

Iraq - on the brink of civil war as recently as 2006-7 - is still plagued by a deadly Sunni Muslim insurgency and Shi'ite militias nearly nine years after the U.S.-led invasion that ousted Saddam Hussein.

Sadr City is a stronghold of radical Shi'ite cleric Moqtada al-Sadr, whose Mehdi Army militia once fought U.S. and Iraqi troops. He is now a key ally of Maliki.

Baghdad's health statistics department put the final toll from the Kadhimiya blasts at 16 killed and 36 wounded and said 13 were killed and 32 others wounded in the Sadr City attacks.

It is early to point our fingers to a particular side till we clarify some issues related to the investigations, said Baghdad operations centre spokesman Qassim al-Moussawi.

We are in a battlefield with the terrorists ... and with the enemies of the political process, so we do not consider these (explosions) as a surprise for us or something strange. We are used to such (insurgent) operations.

Moussawi put the toll from the Sadr City attack at 33 wounded and said 29 were wounded in the Kadhimiya bombings. He said he did not have figures for the number of people killed.

MALIKI MOVE

Maliki asked parliament to have his Sunni deputy Saleh al-Mutlaq removed nearly three weeks ago and sought the arrest of Sunni Vice President Tareq al-Hashemi on charges he ran death squads.

On Tuesday, members of the Sunni-backed Iraqiya bloc boycotted Iraq's parliament and cabinet, accusing Maliki's bloc of governing alone in a power-sharing coalition that was supposed to ease sectarian tensions.

The inclusion of Iraqiya in the governing coalition was widely considered crucial to prevent a return to the level of sectarian violence that was unleashed after the 2003 U.S.-led invasion. Thousands were killed in the violence.

Many Sunnis complain of having been sidelined in the political process since Saddam was ousted and the majority Shi'ites dominated the government.

John Drake, a senior risk consultant with AKE Group, said it was likely Shi'ites would continue to be targeted in coming weeks ahead of Arbain, a major Shi'ite Muslim religious rite.

(Additional reporting by Aseel Kami; Writing by Serena Chaudhry; Editing by Louise Ireland)