At least 60 people have been killed and 123 wounded after a suicide bomber blew himself up outside an army recruitment base in the centre of Baghdad, the media office of the Health Ministry has said.

The blast, which tore through a line of recruits, was one of the bloodiest this year and occurred as suspected insurgents also launched an assassination campaign against judges in the Iraqi capital and a volatile province north of Baghdad.

The bloodshed added to tensions that have simmered following an inconclusive election more than five months ago that has yet to produce a new government.

Insurgents have been targeting Iraqi police and soldiers as they prepare to take full responsibility for security on September 1, when the United States ends a seven-and-a-half-year combat mission.

US troop numbers will be reduced to 50,000 for a training mission before a full withdrawal planned for next year.