Basra:  Iraq's US-backed Prime Minister Nouri Al Maliki vowed on Thursday security forces would battle Shiite militia in Basra "to the end" despite thousands of protesters marching to demand his resignation.

Mahdi Army fighters loyal to cleric Moqtada Al Sadr remained in control of the streets of Basra, Iraq's second biggest city and main oil hub, defying a three-day government offensive that has led to violence spreading across the south and Baghdad. Saboteurs blew up one of Iraq's two main oil export pipelines from Basra, cutting at least a third of the exports from the city which provides 80 per cent of revenue.

Al Maliki, who has travelled to Basra to oversee the crackdown, told tribal leaders: "We entered this battle with determination and we will continue to the end. No retreat. No talks. No negotiations."

More than 130 people have been killed and hundreds wounded since the government launched its operation on Tuesday, exposing deep divisions between powerful factions within Iraq's Shiite community.

In Washington, US President George W. Bush said it will "take some time" for Iraqi forces to crush Shiite militias but expressed confidence that they would ultimately prevail. "This operation is going to take some time to complete," he said in a speech, adding that "normalcy is returning to Iraq."