Death squad leaders have fled Baghdad to evade capture or killing by U.S. and Iraqi forces before the start of the troop "surge" and security crackdown in the capital.

A former senior Iraqi minister said most of the leaders loyal to Muqtada al-Sadr, the radical anti-American cleric, had gone into hiding in Iran.

Among those said to have fled is Abu Deraa, theShiite militia leader whose appetite for sectarian savagery has been compared to that of Abu Musab al-Zarqawi, the leader of Al Qaeda in Iraq, who was killed last year.

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The former minister, who did not want to be named for security reasons, backed Sunni members of parliaments' claims that Iraqi Prime Minister Nouri al-Maliki had encouraged their flight. He alleged that weapons belonging to Sadr's Mahdi Army had been hidden inside the Iraqi interior ministry to prevent confiscation.

Maliki said last week: "I know that senior criminals have left Baghdad, others have left the country. This is good — this shows that our message is being taken seriously."

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Sadr has been unexpectedly subdued about the coming purge, prompting allegations of a deal between the radical cleric and the Iraqi prime minister.

The flight from Baghdad could impede American plans to target the leaders of death squads. An extra 17,000 US troops are being sent to Baghdad as part of the surge in forces promised by President Bush.

Although Sadr's militia has been promised no quarter, American and Iraqi forces hope to avoid having to fight their way throughShiite strongholds such as Sadr City, home totwo millionimpoverished people.

With Bush facing heavy criticism at home over the surge, death squad leaders have every incentive to wait out what could be the president's last-ditch effort to pacify Baghdad. Zalmay Khalilzad, the outgoing U.S. ambassador to Baghdad, said last week he was concerned that militants were "lying low, avoiding conflict now in order to fight another day".

Maliki's Shi'ite-led government is under heavy pressure from the Americans to demonstrate even-handedness towards the Sunni community, but suspicions remain high.

The White House is concerned that Iran is also strengthening its foothold in Iraq. Bush confirmed on Friday that U.S. forces are now authorized to capture or kill Iranian agents believed to be involved in attacks. Until recently, the policy had been to "catch and release".

"It makes sense that if somebody is trying to harm our troops or stop us from achieving our goals or killing innocent citizens in Iraq that we will stop them," Bush said.

One U.S. official said that Lieutenant-General David Petraeus, who will be in charge of the surge, is planning to designate Iran's Revolutionary Guard a "hostile entity".

According to a U.S. source, American officials fear that Iran is following the path it took in Lebanon during the 1980s, when Islamists were encouraged to leave the relatively moderate Amal group for Hezbollah. The more militant Iranian-backed group went on to overtake Amal in popularity.

The Americans believe Iran is encouraging a similar split in Sadr's forces by sponsoring the most extreme anti-Sunni death squad leaders.

"If Muqtada al-Sadr is not personally enthusiastic about sectarian killings and some militants are acting independently of him, it makes sense to go after the Iranian connection," said Patrick Clawson, an expert on Iraq at the Washington Institute for Near East Policy.

The Bush administration has a "mountain of evidence" of Iranian involvement in Iraq, state department spokesman Sean McCormack said. It hopes to make public as much of the dossier as possible, ideally this week.

But some U.S. officials believe Iran's influence is being exaggerated in order to divert the blame for deteriorating security in Iraq, where more than 150 Iraqis were killed by bomb attacks last week, and seven American soldiers in the past three days.

The sharp criticism of Iran is also designed to persuade Sunni powers such as Saudi Arabia and Egypt that America is attentive to their interests in the region. But the Maliki government is dependent on Sadr for political support.

Mohammed al-Daini, a prominent Sunni member of parliament, last week accused Maliki of bowing to pressure from Tehran by releasing 482 Iranian prisoners in August last year, two days before the Iraqi prime minister traveled to Iran.

"Iran demanded that Maliki free the prisoners before setting foot in the country," al-Daini alleged. "He postponed his visit twice, but he finally agreed."

Al-Daini, who blew the whistle on secret detentions and torture centers linked to Iraqi government officials, has a letter, allegedly signed by Maliki, ordering the prisoners to be freed.

Thafer al-Ani, a second Sunni member of parliament, said he had confronted Maliki over the issue. "He could not deny it as the letter was signed by him," al-Ani said. "Sadly, the real occupier of Iraq is now Iran, not the United States."

Complete coverage is available in FOXNews.com's Iraq Center.