The Iraqi government imposed a curfew in the tense southern town of Amara on Monday after fierce battles between militias and police last week.
Hours before the curfew went into effect, gunmen dragged two police lieutenants from their homes and dumped their bodies on the city's outskirts, a local councillor said.
Clashes between militia and Iraqi security forces, mainly fuelled by tribal divisions, killed at least 25 people last week in Amara, which was handed over by British troops to Iraqi security forces two months ago. The government has ordered its military forces to confront armed groups breaking the law.
"We have imposed the curfew due to the security situation there," Defence Ministry spokesman Mohammed al-Askari said.
Askari said the Defence Ministry was redeploying the army and the curfew, which will remain in force until further notice, would allow soldiers to control Amara.
Defence Minister Abdul Qadir Jassim told local state channel al-Iraqiya the ministry had received intelligence that militias were planning more attacks on police stations.
The government is struggling to exert its authority over militias blamed for reprisal killings and to build a viable police force.
"Lately, unlawful armed operations have increased, which is putting the security and the political stability of the country in danger," a government statement said in a message aimed at the Mehdi Army, a militia loyal to powerful cleric Moqtada al-Sadr.
"Everybody should know that orders were given to our armed forces to confront any attempts at violating the law, whoever is the source."
MORE ATTACKS PLANNED
British military spokesman Major Charlie Burbridge said there were around 3,000 Iraqi soldiers in Amara to patrol the streets. British forces have a 600-strong contingent on standby in the outskirts of the town.
"The situation is very tense ... violence could erupt at any time," he said.
The clashes in Amara between Sadr's militias and police forces under the command of the rival Badr Brigades have exposed a power struggle in the ruling Shia coalition that threatens to further complicate US efforts in Iraq.
Under mounting US pressure, Prime Minister Nuri al-Maliki has pledged to disband militias including the Mehdi Army.
But Maliki, is politically dependent on parties with ties to the militias. Sadr has a large block in parliament which provides key support to Maliki's coalition and moving against him could weaken Maliki's five-month-old government.
Maliki last week met Sadr and Grand Ayatollah Ali al- Sistani to enlist their support in curbing sectarian violence.