Moqtada Al-Sadr takes break from politics.

BAGHDAD - Iraq's elusive Shiite cleric Moqtada Sadr has decided to drop out of politics for the time being because his disillusionment with the political scene in Iraq has left him sick and anxious, he said in an unusually personal letter to his followers released Friday.

In a written response to a query from a group of followers asking why he hadn't been seen in public for so long, Sadr said More..he had decided to devote himself to a period of study, reflection and prayer after failing in his core mission to rid Iraq of the U.S. occupation or to turn it into an Islamic society.

He also cited the betrayal of some followers, whom he accused of falling prey to "materialistic" politics.

"So far I did not succeed either to liberate Iraq or make it an Islamic society -- whether because of my own inability or the inability of society, only God knows," Sadr wrote.

"The continued presence of the occupiers, on the one hand, and the disobedience of many on the other, pushed me to isolate myself in protest. I gave society a big proportion of my life. Even my body became weaker, I got more sicknesses."

Speculation has been intensifying as to the whereabouts of the maverick cleric, whose Mahdi Army militia twice fought U.S. troops in 2004 and then was accused of many of the sectarian killings of Sunnis that pushed Iraq to the brink of civil war.

His last public statement came two weeks ago, when he renewed the six-month cease-fire that has been credited with helping bring down the levels of violence in Iraq.

But he has not been seen in public since May. Sadrist officials said in January that he was studying to become an ayatollah in the holy city of Najaf, a position that would give the 30-something leader greater religious authority over the movement he inherited from his slain father. The U.S. military and some Iraqi officials say he is living in the Iranian city of Qom.

This was the first time Sadr has sought to explain his absence, which had given rise to speculation that he was no longer exerting full control over the Mahdi Army.

Sadr's chief spokesman, Sheik Salah al-Obeidi, disputed suggestions that the letter's doleful tone suggested Sadr is contemplating a prolonged absence from politics.

"He remains actively involved in the political field and will return when the time is right," al-Obeidi said, citing the fact that most members of the Mahdi Army have obeyed the cease-fire order as evidence that Sadr commands their loyalty.

The letter came as police raised the death toll in Thursday's double bombing along a busy Baghdad shopping street to 68. It was the bloodiest single attack in Baghdad since the level of violence began to fall last summer, and the U.S. Embassy in a statement blamed Al Qaeda in Iraq.