Iraq's top Shiite Muslim cleric, Grand Ayatollah Ali al-Sistani (search), passed through Beirut on his way to London Friday to receive treatment for a heart condition.

Two Beirut airport security officials said Sistani arrived on a chartered jet from Iraq and departed on a scheduled Middle East Airlines flight for London.

"The ayatollah suffered a health crisis related to his heart a few days ago," Sistani's spokesman in Beirut, Sheik Hamed Khafaf, told The Associated Press on Thursday. "A team of specialist doctors are treating him and providing care."

It was not clear when Sistani suffered his health crisis nor how serious his current state is.

Sistani, who is believed to have suffered heart problems before, lives surrounded only by close relatives and aides in a modest home in Najaf (search), a holy city in southern Iraq that has seen heavy fighting in the last day. His voice carries great political weight with Iraq's majority Shiite Muslims.