US launches offensive in western Iraq

The offensive comes two weeks before a referendum on a new constitution, when US commanders expect a surge in violence across the country similar to that experienced in the first post-Saddam Hussein elections in January.

A regiment of marines, soldiers and sailors launched Operation Iron Fist in the early hours against what the US military called a "known terrorist sanctuary" in the town of Sedea, near Qaim, 12km from Syria.

It is at least the third large-scale offensive US forces have conducted in the area in the past four months. Previous operations appear to have failed, as insurgents have quickly returned to reoccupy the towns and resume guerrilla activities.

"Operation Iron Fist began in the early morning hours with the objectives of rooting out al-Qaeda in Iraq terrorists operating within the area and disrupting insurgent support systems," Marine Captain Jeffrey Pool said in a statement.

"For the past several months, terrorists within Sedea have escalated their intimidation and murder campaign against the local populace and city government officials," he said.

The assault follows a major attack on the northern town of Tal Afar, also considered an insurgent stronghold, last month.

Iraqis will vote in a referendum on a new draft constitution on October 15, despite the threat of attack and amid a general escalation in violence across the country, much of it claimed by al-Qaeda in Iraq, a group headed by Abu Musab al-Zarqawi.

Qaim and Sedea are both in Anbar province, a rebellious Sunni Arab region stretching from Baghdad to the borders with Jordan and Syria and a base of the 2-year-old insurgency.

Sunni Arab politicians strongly oppose several elements in the draft constitution, which was largely drawn up by the Shia and Kurdish parties that dominate the government.

At Abu Ghraib, outside Baghdad, US authorities released a further 500 detainees from the notorious prison as a goodwill gesture to coincide with the holy month of Ramadan, which begins this week. Another 500 were released late last week.