A bomber on Tuesday detonated his explosives-laden truck on a bridge north of Baghdad and killed at least eight people, Iraqi officials said.

The blast partially destroyed the concrete structure of the bridge and sent three civilian cars plunging into the river below, they said.

The bridge on the Thra Dijla river was a key link connecting Baghdad with the town of Taji, around around 40 kilometres (25 miles) to the north in Salaheddin province.

"Rescue teams are searching for survivors from the cars which went down after the attack," a security official said.

Some political observers believe that the presence of foreign occupying forces remains behind insecurity in the oil-rich country.