BAGHDAD, June 4: Four US soldiers were killed on Friday in an attack on their convoy near a Baghdad slum, underscoring the relentless insecurity in Iraq that provoked Russians helping rebuild the country to pull out a third batch of workers.

In Najaf and Kufa, a truce went into place as US forces and Moqtada Sadr's Mehdi Army agreed to withdraw from the streets where they have been fighting for two months. "We have withdrawn our fighters from the streets of Kufa and Najaf," Abu Jafaar, a Sadr aide, said.

In an ominous development, supporters of Moqtada Sadr shouted down a rival at the shrine of Hazrat Ali in Najaf. The four US soldiers were killed and five wounded - an unusually heavy toll for a single incident - when an explosion struck as they travelled on a major highway in Baghdad.

The deaths took the combat death toll since President Bush ordered the invasion of Iraq in March last year to 600. Local witnesses said US vehicles had come under fire from guerillas wielding grenade-launchers.

It was not clear who the attackers were. The incident, which left unidentifiable blazing wreckage on the road, was close to Sadr City, a stronghold of Mehdi Army fighters loyal to Moqtada al Sadr. -AFP/Reuters