Washington ? Anti-American cleric Muqtada al-Sadr fled Iraq for Iran ahead of a security crackdown in Baghdad and the arrival of 21,500 U.S. troops sent by President Bush to quell sectarian violence, a senior U.S. official said Tuesday.

Al-Sadr left his Baghdad stronghold some weeks ago, the official said, and is believed to be in Tehran, where he has family. The official, speaking on condition of anonymity to discuss U.S. monitoring activities, said fractures in al-Sadr’s political and militia operations might be part of the reason for his departure. The move is not believed to be permanent, the official said.

Al-Sadr’s departure was reported by several television networks Tuesday.