Amara: Iraq has sent army and police units to the southern city of Amara as part of a new crackdown against Shiite militias, local officials said on Saturday.

The operation is the latest stage in Prime Minister Nouri Al Maliki's drive to stamp his government's authority on areas of the country previously controlled by Shiite militias or Sunni Arab insurgents.

Adel Al Muhoudir, governor of Maysan province, said, "The decision to undertake the operation has been taken, but the zero hour has not been set yet."

Iraqi tanks were seen on major streets in Amara. Iraqi security forces patrolled and many checkpoints had been set up in the city.

The city is a stronghold of anti-American Shiite cleric Moqtada Al Sadr, who agreed to a ceasefire after US-backed Iraqi forces launched a major crackdown on his Mehdi Army militia in Basra in March.

A spokesman for US forces declined to give details of the operation, saying it was "Iraqi-led and planned".

Iraqi armoured vehicles had arrived from the southern city of Basra and police units had come from Baghdad and elsewhere, the security official said.

Sadr ordered a delegation of clerics to go to Amara for talks with regional officials on how the operation would be carried out, said Sayyid Kareem Al Battat, a delegation member.

Battat said the delegation carried instructions from Sadr for Mehdi Army members to respect the ceasefire ordered by the cleric.