BAGHDAD - 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 US troops withdrew from Iraq. Bombings on December 22 in the predominately Shi'ite parts of Iraq's capital killed 72.Analysis: Al-Maliki - Iraq's next autocrat?Police: Gunmen kill five Iraq Sunni militiaOn 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 laborers 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.