Radical Iraqi cleric Moqtada Sadr has delivered his first public sermon in two months, denouncing interim Prime Minister Iyad Allawi.
Sadr blasted both Allawi and militants who behead foreigners
Speaking at Friday prayers in Kufa mosque, the Shia leader said Mr Allawi had proved that he was only continuing the US-led occupation.
In his first sermon for two months, Mr Sadr also condemned the beheading of foreign hostages seized by militants.
He said such acts would be punished according to Islamic law.
Mr Sadr has repeatedly condemned the presence of foreign troops in Iraq.
He has also argued that the new interim government is illegitimate.
Mr Sadr used harsh language against Mr Allawi.
"Damn him and damn the occupier," he told worshippers in Kufa.
He also took aim at militants here who have decapitated at least three foreigners since April.
"It is illegal according to Islamic law," he said.
Militants have threatened to behead three Kenyans and three Indians and an Egyptian captured in recent days. The militants - calling themselves The Holders of the Black Banners - are demanding that their Kuwaiti employer pull out of Iraq.
Mr Sadr's militia waged fierce battles against the US-led coalition after his paper was closed down and one of his deputies arrested in March.
A ceasefire was reached in June and earlier this month the newspaper was allowed to resume publishing.
In recent weeks Mr Sadr kept a low profile, after US commanders threatened to capture or kill him.