A truck bomb explosion on a bridge in Baghdad has killed at least eight people and sent several cars toppling into the River Tigris below.

The rush-hour blast partially destroyed the Sarafiya Bridge by collapsing one of its girders.

Several people have been hurt in the blast and police are looking for survivors in the river waters.

US and Iraqi troops launched a security sweep in Baghdad two months ago in an effort to reduce sectarian violence.

The truck bomb which had been abandoned on the span of the bridge exploded at 0700 local time (0300 GMT), just as traffic was starting to get heavier with the approach of the rush hour.

The Sarafiya bridge was one of the busiest links across the Tigris, the main connection for the northern part of the city. Many bridges in Baghdad have checkpoints at either end.

It was built by the British in the 1920s and damaged by American bombing in 1991.

US commanders say the number of civilians being killed in the city has fallen for the third month running, but there has been a rise in the number of violent deaths outside the city.

However, the BBC's Jim Muir in Baghdad says so far the security surge has not been able to halt the bomb attacks, which have continued virtually every day.

PHOTO CAPTION

US soldiers secure the area at Baghdad's collapsed Al-Sarafiyah bridge. (AFP)

BBC