An anti-American cleric whose militia was once the nemesis of US troops in Iraq says that his followers are still resisting the US enemy with all means.

But Muqtada al-Sadr, now a formidable force in Iraqi politics and not just a militia leader, tempered his fiery words by saying the new Iraqi government should be given a chance to get American forces out of the country in a "suitable" way.

In his first speech since returning from almost four years of self-imposed exile in Iran, the 37-year-old cleric, whose Shiite militias once battled US troops and terrorised Iraqi Sunnis, stopped short of explicitly urging violence against Americans.

However, he left open the possibility that some 50,000 US troops in Iraq could be targeted before they are set to leave at the end of this year.

"Let the whole world hear that we reject America. No, no to the occupier," al-Sadr said during a 35-minute speech in Najaf, a holy Shiite city about 100 miles (160km) south of Baghdad.

"We don't kill Iraqis - our hands do not kill Iraqis. But we target only the occupier with all the means of resistance," he added.

"We are still resisters and we are still resisting the occupier militarily and culturally and by all the means of resistance."

Al-Sadr has long branded the US military as occupiers in Iraq, and Washington considers him a security threat. Yet, after winning 40 seats in March parliamentary elections - and taking eight top leadership posts in the new government - al-Sadr's political muscle makes him a force that cannot be ignored.

Addressing an adoring and frenzied crowd of thousands, al-Sadr called the US, Israel and Britain "our common enemies".

"Maybe during the past few days and months, we forgot the resistance and the expel of the occupier as we were busy with politics," al-Sadr said.