Radical Shiite cleric Muqtada al-Sadr threatened last night to unleash suicide bombers if US troops move against him in Iraq's holiest Shiite city, and his militiamen attacked a Bulgarian convoy, killing a soldier.
Meanwhile, police in Basra arrested five Iraqis believed linked to al-Qaida and suspected in brutal suicide bombings Wednesday that killed 74 people.
The five men were captured with a total of nearly 25 tons of TNT, and police were looking for another car bomb they suspected was somewhere in the mainly Shiite city in the far south of Iraq, said Basra's police intelligence chief Khalaf al-Badran.
US forces massed on the outskirts of Najaf have said they have no intention of moving in for the time being to capture al-Sadr fully aware that an American entry into the holy city would spark a wave of outrage among Iraq's Shiite Muslim majority.
But al-Sadr's comments and the bloody clash in the nearby city of Karbala were a show of defiance amid off-and-on negotiations aimed at trying to resolve the standoff.
The Karbala fighting brought the first coalition death in fighting with al-Sadr followers in more than a week.
"Some of the Mujahedeen (holy warrior) brothers have told me they want to carry out martyrdom attacks but I am postponing this," al-Sadr told thousands of worshippers during his Friday prayer sermon at the main mosque in Kufa, near Najaf.
"When we are forced to do so and when our city and holy sites are attacked, we will all be time bombs in the face of the enemy," he said.
Suicide bombings would be a new tactic for al-Sadr, whose followers launched a bloody revolt in early April, attacking coalition troops across the south. Al-Sadr, however, is known for blustery rhetoric and threats and is under pressure from moderate Shiite clerics to resolve the standoff.
In his sermon, al-Sadr condemned suicide bombings Wednesday in the southern city of Basra because they targeted civilians and Iraqi police. The death toll from those attacks rose to 74, including at least 16 children killedn when their school buses were incinerated in the blasts.