At least 13 Iraqi army recruits have been killed and one wounded in a suicide bomb attack on their minibus in Baghdad, officials said.
The attack happened near the Muthenna recruitment centre which has been targeted by insurgents in the past.
The bomber, who was wearing an explosive belt, is reported to have boarded the bus at the centre.
Witnesses heard two loud blasts and saw a plume of white smoke close to the north gate of the former air base.
The gate is where recruits wait for shuttle buses to take them to the capital's main bus station.
They had just signed forms to join the army and had got on the bus to be taken to their homes, the BBC's James Shaw in Baghdad reports.
The base, in the western part of the city, is the main recruitment and training centre for the Iraqi army in Baghdad.
At least 30 people died in two separate attacks on the base in July.
On Sunday, four people were killed in two car bomb blasts in Baghdad.
The violence comes amid a joint operation by US and Iraqi forces to restore security in the capital.