The attack on a minibus - an inexpensive mode of transport for Baghdad residents - took place in an area close to the sprawling Shia slum of Sadr City.

Three Iraqi policemen were also killed and three others wounded when a bomber blew himself up next to a checkpoint at the entrance to a university in Ramadi, the capital of the Sunni-dominated al-Anbar province, a local police source said.

Iraqi security forces are frequent targets of attacks.

On Sunday, seven policemen had been killed in a suicide bombing during a police parade in Diyala province.