Sadr, whose movement battled US forces in Iraq, also voiced opposition to American military advisers meeting with Iraqi commanders combatting an offensive that has overrun swathes of five provinces, killed more than 1,100 people, displaced hundreds of thousands and threatens to tear the country apart -- ideologically and geographically.
Prime Minister Nuri al-Maliki has meanwhile warned rivals against exploiting the crisis to sideline him after Washington urged Iraq's fractious political leaders to unite in the face of an onslaught led by the jihadist Islamic State of Iraq and the Levant.
"We will shake the ground under the feet of ignorance and extremism," Sadr said in a televised speech from the Shiite holy city of Najaf.
He said foreign powers "and especially forces of the occupier and regional states should take their hands off" the country, referring to the US and Iraq's neighbours.
In an apparent effort to restrain worsening sectarian tensions, however, Sadr insisted that the militants did not represent Iraqi Sunnis, whom he said had suffered "marginalisation and exclusion".
The cleric demanded "new faces" in a national unity government following April 30 elections that saw incumbent prime minister Maliki emerge with by far the most seats, albeit short of a majority.
Opponents of Maliki have called for a "salvation" government to be formed that would largely ignore the election results, which they describe as a sham, but the premier has said such a move would be a "coup against the constitution and the political process".