Sadr has threatened to wage "open war" on the Baghdad government if it does not halt operations against his supporters.
Moqtada Sadr said he was giving the government a "last warning", and urged it to take "the path of peace".
His statement came as Iraqi troops, with US and UK support, clashed with his forces in Baghdad and the south.
Moqtada Sadr issued the warning after soldiers launched fresh operations against positions being held by his Mehdi Army.
The BBC's Crispin Thorold in Baghdad says the government is slowly beginning to establish a presence in areas where the Mehdi Army had been all-powerful.
http://news.bbc.co.uk/2/hi/middle_east/7356875.stm
It is nice to hear that this guy now has to plead with the government, not too long ago it was the other way around.