At least six people have been killed and 35 wounded in two separate attacks in Baghdad.

In the first of the two attacks, three policemen and one civilian were killed when a parked car bomb exploded near a bus station in Baghdad's southern Bayaa neighbourhood.

A second bomb targeting police and rescue services arriving at the blast site detonated minutes later.

In the Sheikh Omar neighbourhood in eastern Baghdad, two bombs near a bus station went off simultaneously, killing two civilians and wounding 12 others.

In a separate development, a senior Iraqi military intelligence official said that authorities had opened an investigation into an incident on the previous day when an Iraqi soldier opened fire on a group of American troops.

The US soldiers had been protecting one of their commanders during a visit to an Iraqi army base about 130 miles north of Baghdad.

Two American soldiers were killed, the first US servicemen to die since President Barack Obama declared an end to combat operations in Iraq last week.