A series of explosions have been reported in central Baghdad on Monday night in an area that is home to several coalition headquarters buildings.

The explosions may have come from mortar shells, officials said.

Earlier Monday, a blast near a holy Shiite Muslim (searchshrine in the city of Karbala killed three people and injured 12, witnesses said.

The Karbala blast occurred on a busy street less than 100 yards from the gold-domed Imam Hussein shrine in the city, 65 miles south of the Iraqi capital, said Mohammed Abu Jaffar al-Assadi, a Shiite cleric.

All the dead apparently were passers-by. He said the bomb had apparently been planted in a parked car. It was not immediately possible to get confirmation of the report from Iraqi police or the U.S.-led coalition.

In Baghdad, five strong explosions were heard in quick succession at about 9:10 p.m., and it appeared the blasts were coming from the western side of the Tigris River (search).

Soon after, the U.S military command reported three or four mortar impacts in central Baghdad.

Karbala was rocked by deadly clashes last month between supporters of rival Shiite factions. Also in October, supporters of a little-known Shiite cleric based in Karbala killed three U.S. soldiers in a rare clash between residents of the holy city and the U.S. military.

On Aug. 29, a car bomb exploded outside a mosque in the nearby city of Najaf, killing more than 85 people including Shiite leader Ayatollah Mohammed Baqir al-Hakim. It was the bloodiest incident since the end of the U.S.-led invasion that overthrew Saddam Hussein.

The Associated Press contributed to this report.