Explosions boomed and gunfire crackled across Iraq's holy city of Najaf on Sunday, marking the resumption of fierce clashes pitting US forces and radical Shiite cleric Moqtada al-Sadr's Mehdi Army, the Dubai-based al-Arabiya TV channel reported.

According to the channel, US army was moving toward the city center.

Witnesses also reported explosions were heard and plumes of smoke seen rising from the old cemetery, north of the Imam Ali Mosque where the firebrand cleric and his followers had been holed up during a major US offensive starting from Thursday.

The renewed battle came one day after truce talks between the Iraqi interim government, the US forces and Sadr's militia collapsed, with the militia blaming Prime Minister Iyad Allawi for backing down at the last minute.

After the talks broke down, the interim government declared to continue military operations in Najaf and urged all media to withdraw from the city by mid-day (0800GMT).

The fresh military confrontation in Najaf, home to 600,000 citizens and one of the holiest cities for the world's Shiite Muslims, also coincided with the opening of an Iraqi national conference beset by delay, boycott, mass walkout and bombing.

The conference, drawing more than 1,000 delegates from various political, civic and religious groups across Iraq, was originally planned to be held in late July, only to be postponed under the United Nations' advice citing precarious security.

The interim Iraqi government called upon Sadr to participate in the meeting, designed to pick a 100-member national assembly tasked with overseeing the caretaker government till the general elections in January 2005.

However, both Sadr and the Association of Muslim Scholars, an influential Sunni body, boycotted the conference, labelling it not representative.

The conference suffered another embarrassment when a group of delegates stages walkout en masse in protest against the ongoing military operation in Najaf.

To worsen the situation, just hours after the opening of the three-day conference, explosions rattled the so-called Green Zonein Baghdad, the meeting venue as well as seat of the interim Iraqi government and the US embassy.

Source: Agencies