Iraq's government has reinforced army and police units in the southern city of Amara ahead of an expected crackdown on Shia militias.
Convoys including armored vehicles and tanks were moving through the northern side of the city, according to reports.
The operation, which officials say will start on Thursday, is the latest stage in Prime Minister Nuri al-Maliki's drive to stamp his government's authority on areas previously controlled by Shia militias or Sunni Arab insurgents.
Army Major-General Tareq Abdel Wahab, leader of the security operation, said government forces had a list of hundreds of "outlaws, criminal gangs and those who violate security" it would hunt down.
Amara is a stronghold of Shia cleric Moqtada al-Sadr, who agreed to a ceasefire after US-backed Iraqi forces launched a major offensive on his Mehdi Army militia in Basra in March.
Past US-led military operations in the area have targeted militants smuggling weapons from nearby Iran.
Perceived by some as lacking the resolve and charisma needed to stabilize Iraq, Maliki has gained respect at home and abroad with security offensives that have helped reduce violence to the lowest level in over four years.
Success in Amara could boost Maliki's image ahead of provincial elections, due on October 1, seen as the battleground for a power struggle that could redraw Iraq's political map.
Apart from taking on Sadr's fighters, Maliki has made substantial gains against al Qaeda, which US and Iraqi officials say is on the run in Iraq.
"The operation in all of Maysan province will impose the law and regain prestige for the state as we did in Basra," Defence Ministry spokesman Mohammed al-Askari told reporters.
The Iraqi-led operations underscore the Shia-led government's desire to take more control of security from the 150,000 US troops in the country.
A Defence Ministry spokesman said Iraq would take security responsibility for the southern province of Qadisiya from US forces in July. The province, relatively quiet in recent months, would be the 10th of Iraq's 18 provinces to return to Iraqi control.