BAGHDAD -- In a darkened living room in the Shia neighborhood of Sadr City, a gray-haired militia commander picked up his phone Friday to read a text message from one of his colleagues on the battlefield.
"Captured six ISIS members in an ambush," it said, referring to militants from the Islamic State of Iraq and Syria, also known as the Islamic State of Iraq and the Levant, an al-Qaida splinter group whose advance over the past 10 days has nearly brought the Iraqi state to its knees. "At dawn I killed two, four I gave to the army."
The message was an example of what members of Iraq's Shia militias describe as growing cooperation with the country's army. As Iraq spirals into chaos, Prime Minister Nouri al-Maliki is relying on the militias -- which once carried out hundreds of attacks on U.S. soldiers -- to help him cling to power.
The lines between Shia militias and the Iraqi armed forces have been increasingly blurred since the withdrawal of U.S. troops in 2011. Now, as the ISIL threat reinvigorates militias and the United States dispatches 300 military advisers to the fracturing country, the overlap is raising questions about increased American support for Iraqi forces.
"Potentially what this could amount to is the U.S. arming or advising Iranian proxies, some of which are on the terror list," said Phillip Smyth, a researcher at the University of Maryland specializing in Shia Islamist groups.
Speaking in London, retired Gen. David Petraeus, the former head of coalition forces in Iraq, raised similar concerns in a speech last week. "This cannot be the United States being the air force of Shia militias," he said of potential U.S. strikes on ISIL targets in Iraq.
A wary White House
The Obama administration is acutely conscious that any direct intervention in the Iraqi conflict could be interpreted as taking the side of Maliki's Shia-dominated government in what is rapidly becoming a sectarian war.
The Iraqi government denies that it allows militias to work within its ranks. But since an estimated 90,000 soldiers shed their uniforms and abandoned their posts as ISIL swept across northern Iraq this month, it has called for new "volunteers" to join the armed forces. That call was followed by a religious decree last week from Iraq's top Shia cleric, Grand Ayatollah Ali al-Sistani, who called for all able-bodied Iraqis to take up arms against the insurgency.
In his decree, al-Sistani urged volunteers to join the regular security forces, a stipulation he reiterated on Friday, saying weapons should remain in the hands of the state.
But many have joined militias instead, as the ISIL sweep, combined with the cleric's call to arms -- even with its stipulations -- spawns a resurgence of the irregular Shia armies that hunted down Sunnis during the bloodiest years of the Iraq War.
A 'systemic' infiltration
While most disbanded, some groups, such as the Iran-backed Asaib Ahl al-Haq and Kataib Hezbollah, which is designated as a terrorist organization by the United States, have remained active since the U.S. withdrawal and have slowly built their presence in the security forces for years.
Smyth described their infiltration as "systemic," raising the possibility that U.S. advisers might soon be working alongside militiamen who once fought them.
The Sadr City commander, who spoke on the condition of anonymity for security reasons, is a follower of firebrand Shia cleric Moqtada al-Sadr, who last week announced the formation of "peace brigades" to repel ISIL attacks on the Shia-majority country's shrines and holy sites.
The brigade is ostensibly a defense force, although the commander's message from his colleague on the front lines near Samarra, about 80 miles north of Baghdad, pointed to a more active role. The commander said the new group is effectively a reincarnation of the Mahdi Army, Sadr's paramilitary force, whose military activities were frozen in 2008.
While Sadr's followers are in the process of organizing, Asaib Ahl al-Haq, which killed and kidnapped numerous American soldiers before the U.S. withdrawal, says it is already actively working within the security forces. The ISIL advance has only strengthened that role, members said.
An influx of religiously motivated recruits and a resurgence of militias at a time of worsening sectarian conflict has raised concern about the potential for an incident that ignites a new round of Sunni-Shia bloodletting.