Grand Ayatollah Ali Husseini al-Sistani, 73, has been in London for medical treatment since Aug. 6, one day after clashes erupted in Najaf. The cleric wields enormous influence among Shiite Iraqis and his return could play a crucial role in stabilizing the nearly three-week-old crisis.

"His eminence Grand Ayatollah al-Sistani will arrive in beloved Iraq in a few hours and he will return to the holy city of Najaf to rescue it from its ordeal," Hamed al-Khafaf said in an e-mail sent to The Associated Press in Beirut.

The announcement came as U.S. and Iraqi forces in Najaf tightened a cordon around the Old City and the neighbouring Imam Ali Shrine, the holiest Shia site in Iraq. U.S. forces shelled militants loyal to rebel Shiite cleric Muqtada al-Sadr in the Old City on Wednesday and smoke rose into the sky after U.S. warplanes pummeled the area overnight.

...

The relentless American bombing in Najaf appeared to be weakening as Iraqi troops moved to within 200 yards of the revered Imam Ali Shrine and Iraq's defence minister once again demanded fighters loyal to a radical cleric surrender or face a violent raid.

The militant force, which once waged fierce battles with U.S. troops throughout the Old City and Najaf's vast cemetery, seemed considerably diminished in number and less aggressive Tuesday after days of U.S. air strikes and heavy artillery pounding.

Hundreds of insurgents have been spotted leaving Najaf in recent days, witnesses said. Those that remained appeared to have pulled back to the area around the shrine, where the fighting Tuesday was concentrated, U.S. troops said.

Al-Khafaf told the Arab satellite television station Al-Arabiya that al-Sistani "will lead thousands of followers on a march to holy Najaf."