Mosul in lockdown

US forces sealed off entire districts of the Iraqi city of Mosul yesterday, blocking bridges and raiding homes in a hunt for suspects after an attack that killed 18 Americans and four other people.

FBI and other experts flown in from Baghdad were probing the cause of Tuesday's lunchtime explosion at a US base mess tent, the deadliest strike on Americans in Iraq. The military declined comment on a report they found the remains of a suicide bomber.

If true, it would pose grave questions for security at US bases as troops prepare to guard Iraq's election next month.

Mosul's governor issued an overnight order on television banning use of the five bridges over the River Tigris and said anyone breaking the order would be shot. Residents said Iraq's third city was a virtual ghost town, with no one in the streets.

A loud explosion hit the west of the city after dark. The cause was not clear, and a US military spokesman said he was aware of it but no US forces or equipment had been damaged.

The military declined comment on an ABC television report that investigators found evidence that a suicide bomber carried out the deadliest attack on Americans since they invaded Iraq.

"Investigators at the base have found remnants of a torso and a suicide vest that was probably a backpack," ABC said, lending weight to a claim by Iraq's Ansar al-Sunna guerillas.

Revised details on casualties referred to an unidentified non-American civilian. US bases employ many Iraqi and foreign workers, including in their privately run catering facilities.

Lieutenant-Colonel Paul Hastings, a spokesman in Mosul, said no conclusion had been reached on the cause of a blast initially blamed on a mortar: "It is still under investigation."

There was joy in Paris when two French journalists, freed after four months as hostages in Iraq, returned to a heroes' welcome. The relieved French government basked in national acclaim and denied paying a ransom, although opponents demanded to know why it took France, which opposed the US war in Iraq, so long to persuade the militants to free the reporters.

President Jacques Chirac and Prime Minister Jean-Pierre Raffarin met Georges Malbrunot and Christian Chesnot when they arrived at a military airport.

The US military said that aside from the unidentified person, the dead were 13 soldiers, five American civilians and three Iraqi National Guards. Four employees of the US oil service firm Halliburton were killed, the company said.

US officials initially said rocket and mortar rounds were fired but Ansar al-Sunna credited one of its "martyrs" and the US commander in Mosul said there was only one explosion.

US operations left Mosul's streets largely deserted. "Students went to school but were told to go home. People went to the shops, saw American troops in the streets, and went home," said Ahmad, 25, a Mosul car dealer too anxious to give his surname. "The place is shut down," said another worried resident, adding that mosques and markets were virtually empty.

"We are conducting offensive operations to target specific objectives," Mr Hastings said.

The attack has raised fears of a new guerilla offensive before next month's election, six weeks after US troops stormed the rebel stronghold of Falluja in a bid to crush the insurgency. Hitherto quiet Mosul has seen near anarchy since.

Witnesses said US forces, backed by Iraqi National Guards, sealed off neighbourhoods in western and southeastern Mosul and raided homes. "They're looking in the areas that are known hotspots," one resident in the west of the city said.

Forty-four of the revised toll of 69 wounded were US soldiers. Some were taken to a military hospital in Germany, eight in critical condition, hospital staff said. The previous costliest incident for Americans was last year when two helicopters came down in Mosul killing 17 soldiers.