A car bomb exploded Thursday near a sacred shrine in the Shiite holy city of Najaf, killing at least four people and injuring about 30, police and health officials said.

The blast occurred about 300 yards from the Imam Ali shrine, police chief Maj. Gen. Abbas Miadal said. The shrine is among the world's most sacred sites for Shiite Muslims and contains the tomb of the Prophet Muhammad's son-in-law, Imam Ali.

Dr. Munther al-Ethari, director of the city's health services, said first reports showed four people were killed and about 30 were injured.

Such attacks are rare in Najaf, which is tightly controlled by police and Shiite security guards. Iraqi Shiites consider any attacks within Najaf as a grave provocation.