BAGHDAD - Fighting erupted Tuesday between rival Shiite militias in Karbala during a religious festival, claiming 51 lives and forcing officials to abort the celebrations and order up to 1 million Shiite pilgrims to leave the southern city.

Security officials said Mahdi Army gunmen loyal to radical cleric Muqtada al-Sadr fired on guards around two shrines protected by the Badr Brigade, the armed wing of the Supreme Islamic Iraqi Council.

Residents of Karbala contacted by telephone said snipers were firing on Iraqi security forces from rooftops. Explosions and the rattle of automatic weapons fire could be heard during telephone calls to reporters in the city 50 miles south of Baghdad.

In addition to the deaths, security officials said at least 247 people were wounded, including women and children.

The clashes appeared to be part of a power struggle among Shiite groups in the sect's southern Iraqi heartland, which includes the bulk of the country's vast oil wealth.

Interior Ministry spokesman Maj. Gen. Abdul-Karim Khalaf said entrances and exits to Karbala "have been secured and more forces are on the way from other provinces." Officials said buses were sent to evacuate pilgrims from the city, which includes some of the world's most sacred Shiite shrines.

Gunfights also broke out Tuesday between Mahdi militiamen and followers of the Supreme Council in at least two Shiite neighborhoods of Baghdad and in Kut, about 100 miles southeast of the capital, police said.