Sadr issued a statement through his offices in Sadr City last week condemning the bilateral security accord between Washington and Baghdad, which U.S. Ambassador to Iraq Ryan Crocker signed Monday with Iraqi Foreign Minister Hoshyar Zebari.

In statements during Friday prayers, the anti-American cleric called on "the honorable resistance fighters" to resume operations against the U.S. occupation if they did not withdrawal from Iraq. He called his unit, reportedly consisting in part of so-called Iranian-backed special groups fighters, The Promised Day Brigade.

In comments to London's Asharq al-Awsat newspaper, residents of the southern port city of Basra, once a stronghold of Shiite militias, expressed concern Sadr's statements pointed to tumultuous times ahead.

Sadr "declared that the resistance through the Promised Day Brigade would not target civilians and security organs, but our past experiences prove otherwise," said Basra taxi driver Sahib Akkab Ali.

Others said past experiences in Basra suggest a return to violence is not beyond comprehension.

Iraqi Staff Maj. Gen. Muhammad Jawad Huwaydi said any opposition to the security agreement with Washington "should go through negotiations and not the use of weapons," which Iraqi Prime Minister Nouri al-Maliki banned for non-government militias following a series of military crackdowns during the summer.