Four people were killed in violence across Iraq on Tuesday, police officials said, one day after a series of attacks left 18 dead. In Mosul, 350 kilometres (218 miles) north of Baghdad a Sunni Imam was killed by a sticky bomb placed on his car, a police officer said. A policeman manning a checkpoint in the restive northern city was later killed by gunmen, the officer said, adding that three more police had been wounded by a bomb in central Mosul. In Baquba, the capital of Diyala province, meanwhile, a former soldier was killed by two gunmen, police said. A bomb in Baghdad caused Tuesday's fourth death. Separately, Major General Qassim Atta, spokesman for the Iraqi Army's Baghdad operations, said security forces shot dead a would-be suicide car bomber in the south of the capital. The car exploded but there were no casualties. 