Top Sadrist Arrested in Amarah

Among those arrested is Amara's mayor, Rafi Abdul Jabbar, who is a supporter of the Shia cleric Moqtada Sadr.

The Sadr office in Amara has accused the Iraqi forces of targeting his group, and ignoring government orders to detain only wanted men.

The Iraqi authorities say troops have recovered a number of weapons.

Correspondents say there has been no shooting so far. A number of armed men avoided arrest by throwing their weapons into the street or canals.

Police have imposed curfews in certain areas, but said government offices, schools and colleges would not be affected.

The operation, which is backed by US forces, has been called Promise of Peace and a government statement said it would "impose law... and confront outlaws".

"We are glad they are bringing stability to the city," said one resident, quoted by Reuters news agency, as the police were searching his house.

British troops handed control of the 250,000-inhabitant city to Iraqi forces in April 2007, but security has remained fragile and militia activity intense.