In a national broadcast Maliki said militants will face "the toughest penalties" if they don't hand over their weapons to the nearest security station and vow to refrain from terrorist activities, reported KUNA, the Kuwaiti news agency.

Basra was the scene Tuesday of heavy fighting in which medical personnel said at least 40 people died and another 200 were wounded. Maliki and his defense and interior ministers were in the southern city to oversee the operation.

Clashes broke out between the government forces and militiamen of the radical cleric Moqtada Sadr at various locations in the city, KUNA said.

U.S. and British jets provided air support for the Iraqi military, The New York Times (NYSE:NYT) reported. No Western forces had entered the city, a British army spokesman said, noting the operation involved nearly 30,000 Iraqi troops and police forces were in Basra and more were arriving.

"They are clearing the city block by block," British Maj. Tom Holloway said.