"We will not be silent in front of this threat," the cleric warned in a statement issued by his office in the holy city of Najaf.

Vowing to defend the people of Kurdistan, Sadr called on the people of Turkey to stop their armed forces from carrying out cross-border shellings in Iraq.

"We are ready to mediate with Turkey to end this crisis. Turkish people have to reject such actions and help to stamp out the fire between the two Muslim nations," Sadr said.

"I hope Turkey will not repeat such bombardments of Iraqi territory. It has no right to do it."

Sadr commands the Mahdi Army, a militia of tens of thousands of young, impoverished Shiites, who are accused of spearheading a sectarian conflict against Iraq's minority Sunnis.

On Saturday, Iraq lodged an official complaint with Turkey claiming it had bombarded the northern Kurdish region.

A Kurdish security official told AFP that Turkish forces had shelled villages in the northern Dohuk province of Iraq early Saturday to flush out rebels from the Kurdistan Workers Party (PKK).

Turkey says the PKK, whose two-decade-old insurgency in eastern and southeastern Turkey has claimed more than 37,000 lives, is acting under the protection of Iraqi Kurds of Kurdistan.

Violence increased with the spring thaw as rebels hiding in the rugged mountains of northern Iraq slipped back across the border to attack Turkish troops, effectively ending a unilateral ceasefire the PKK declared in October 2006.

Turkey maintains a 1,500-strong troop presence several kilometres (miles) inside Iraq to try to stem the flow of PKK fighters across the mountainous 384-kilometre (240-mile) border.

It has repeatedly demanded tougher action from Iraq and the United States against the rebels and refuses to rule out acting unilaterally if its demands are not heeded.