IRAQI Prime Minister Ibrahim al-Jaafari said yesterday that foreign fighters regularly slip into Iraq from Syria and called on authorities there to do more to stop them as five US troops were killed.

Hundreds of Iraqi police and army troops fanned out across Baghdad yesterday, setting up checkpoints and fortifying polling stations with barbed wire and blast barriers two days ahead of a historic constitutional referendum.

IRAQ prepared to seal itself off from the outside world yesterday and clamp down on movement around the country to ward off threats from insurgents bent on wrecking a referendum on a new constitution.

US and Iraqi forces stepped up security across Iraq today and prepared to impose an overnight curfew in an effort to reduce insurgent attacks aimed at wrecking this weekend’s constitutional referendum.

US troops killed 11 Iraqis who ambushed a convoy outside Baghdad yesterday. It was one of the most intense clashes yet in the daily grind of attacks on American forces.