U.S. and Iraqi officials have also alleged that the Iranians use members of Lebanon's Shiite movement Hezbollah to train Iraqi Shiite militants. Hezbollah has denied the allegation.

Sunni politicians have long protested that efforts to purge ex-members of Saddam's Sunni-dominated Baath Party from the government and military were used to exclude Sunnis from political life in Iraq and expand Iranian influence.

The United States launched the effort to remove senior Baath figures from public life shortly after the 2003 invasion. Last January, however, parliament approved legislation relaxing the ban in a U.S.-backed move to reconcile Shiites and Sunnis.

But many Shiites, who suffered under the former regime, resent any moves to restore Baath Party figures to government jobs, especially those in the security services.

Last month, a government report shown to The Associated Press showed that 123 former intelligence and security officers had been quietly reinstated into their jobs after the new law went into effect.

Reaction to al-Lami's arrest was sharply divided along sectarian lines.

Ahmad Chalabi, a secular Shiite and former Pentagon favorite once viewed by Washington as a possible successor to Saddam, condemned the arrest, saying that al-Lami had played "a great essential role" in "fighting and confronting Saddam's regime despite the risks that surrounded him."

Chalabi, who spearheaded the first moves against Baath members, called for al-Lami's release and said in a statement that his arrest showed that U.S.-led forces pay "no attention to Iraqi human rights."

But Sunni legislator Mohammed al-Daini accused al-Lami and others of sectarian bias and links to Iran.

"The Americans know very well that such people were brought up and trained in Iranian intelligence system," al-Daini said without offering evidence. "The detention of al-Lami is part of a chain of events that will lead to the uncovering of others."

Salim Abdullah al-Jubouri, spokesman for the main Sunni bloc in parliament, said the Sunni community was "looking forward to the results of the investigation" into al-Lami's arrest because "it is unlikely that he was working alone."

U.S. military attention believes the special groups are breakaway factions of the Mahdi Army of anti-American cleric Muqtada al-Sadr, who is now in Iran. Al-Sadr ordered a cease-fire in August 2007 but some factions refused to accept the order and have continued attacks.

On Thursday, al-Sadr released a statement saying his largely disbanded Mahdi Army militia would extend that cease-fire "until further notice" and that anyone who violates the truce would no longer be considered part of his militia.

Last month, al-Sadr announced he was transforming his militia into a social welfare body with a few guerrilla cells to attack U.S. troops if Washington doesn't agree to leave Iraq. The announcement followed setbacks in battles with the U.S.-supported Iraqi army in Baghdad, Basra and Amarah.

Separately, the U.S. military said an American soldier died of wounds he received after coming under fire while patrolling northern Baghdad on Wednesday. Another U.S. soldier was killed in a roadside bomb attack while on patrol Thursday in Baghdad, the military said.