Iraqi Shiites increasingly fear the Muslim sect and its holy sites could be targeted in neighboring Syria as the civil war there takes on increasingly sectarian overtones, and Iranian-backed militants are girding for violence in both countries, according to Shiite leaders and government officials.

The Iraqi concerns center on the role ultraconservative Sunnis might play in Syria should President Bashar Assad be forced from power, and on what they see as growing threats to the revered Sayyida Zainab mosque complex outside Damascus.

The golden-domed shrine is believed to house the grave of the Prophet Muhammad's granddaughter and is one of Shiite Islam's holiest sites. It was damaged in June when a suicide bomber blew up an explosives-packed van nearby, and Sunni hard-liners have threatened to destroy it since.

Many Iraqi Shiites are haunted by memories of the 2006 bombing of the al-Askari shrine in the Iraqi city of Samarra. That attack was blamed on al-Qaida in Iraq and set off years of retaliatory bloodshed between Sunni and Shiite extremists that left thousands of Iraqis dead and pushed the country to the brink of civil war.

"We have real concerns that the Samarra attacks will be repeated" at the Zainab shrine, said Saleh al-Haidari, the head of Iraq's Shiite endowment. "The retaliation could be huge and very violent."

Violence in Iraq, where the Shiite majority rose to power following the ouster of Saddam Hussein's Sunni-dominated regime after the 2003 U.S.-led invasion, has fallen sharply in recent years. There have been several major attacks on Shiite targets blamed on Sunni insurgents, but so far Shiite militants have not responded in force.

Iraqi officials fear the shift in Syria's power balance could change that.

An official in the Badr organization, a conservative Shiite bloc that is part of Iraqi Prime Minister Nouri al-Maliki's ruling coalition, said Shiite militant groups have acquired new advanced and heavy weapons and were gearing up for a fierce reaction if the Zainab shrine were hit. The official spoke on condition of anonymity because of security concerns.

A Shiite militant who described himself as a member of the anti-U.S. cleric Muqtada al-Sadr's Mahdi Army militia said about 200 Iraqi fighters drawn from the ranks of various Shiite militias, including Asaib Ahl al-Haq and the Hezbollah Brigades, have made their way to Syria in order to protect shrines there.

Lebanon's Iran-backed Hezbollah militia is also believed to be sending fighters to help the Assad regime, which is dominated by Alawites, an offshoot of Shiite Islam.

The 42 year old militant, who agreed to be identified only by the nickname of Abu Zainab because the Mahdi Army is officially no longer supposed to be engaged in military activities, said the fighters are being supported by Iran and consider the defense of the holy sites to be a religious duty. "They are happy to do this," he said.

Iran has been providing logistical support and small arms to volunteer fighters guarding the shrine, the militant said.

Tehran has long denied supporting violence in Iraq, although it has seen its influence rise since American troops withdrew in December.

It is extremely difficult to independently verify the Iraqis' claims. Some officials downplayed the suggestion that Iraqi militia members had been formally sent to take up arms in Syria in recent months, though they suggested that Iraqi Shiite militants who had settled near the Zainab shrine prior to the Syrian uprising have stayed to defend the site.

Iraqi government spokesman Ali al-Dabbagh said the government is concerned that Shiite holy sites in Syria could be targeted.

"The targeting of these shrines will lead to the eruption of a sectarian volcano in the region. This will set off a sectarian fire that nobody will be able to put out. Certainly, we have great fears about this," he said.

Iraqi officials acknowledge that well-armed Shiite militiamen remain in Iraq, despite efforts to disarm them or integrate them into state security forces.

A senior Iraqi security official estimated there are 2,000 to 3,000 well-trained militiamen in Iraq, and said they have access to hidden caches of heavy weapons. The official, who refused to allow his name to be used because he is not authorized to release the information, said the potential targeting of Shiite shrines in Syria risks provoking not just militias, but "the whole Shiite community."

Even as concerns grow that Iraqi Shiites could be drawn into Syria's civil war, Sunni fighters aligned with al-Qaida's Iraq franchise are believed to be moving back and forth across the Syrian border to help Sunni rebels overthrow Assad, according to senior Iraqi security officials. The group is also setting up training camps for insurgents in Iraq's western deserts, officials say.

"It is very difficult to imagine a scenario could emerge in the long term where you have this continued stalemate (in Syria) and the various factions in Iraq don't get involved," said Aram Nerguizian, a Middle East expert at the Center for Strategic and International Studies in Washington. "Most observers, myself included, are still trying to map out who the players are."

Fear for the fate of Syrian Shiites and the Zainab shrine in particular are palpable among Iraq's Shiite faithful.

Believers point worryingly to statements made in Internet postings and on ultraconservative Sunni satellite channels from the Gulf calling for Zainab's destruction.

While the threats represent a minority, extremist point of view, they are being taken seriously on the streets of Iraq.

Tears welled up in Rasheed al-Sheikh's eyes when he was asked about the Syrian shrine earlier this week. The 75-year-old moneychanger, who does business in Baghdad's Shiite Kazimiyah neighborhood, heard of threats to the shrine from other merchants. He said he fully supported sending fighters to Syria.

"Of course this is a good thing. We all love the shrines," he said, growing emotional at the thought that the holy sites could be harmed. "They (Sunni extremists) are serious about these threats. They've done it many times before."


Associated Press writer Sameer N. Yacoub contributed to this report.