Members of Iraqi security forces and Shiite militia fighters make their way in vehicles from Samarra to the outskirts of Tikrit, north of Baghdad, on Feb. 28. (Reuters)

Shiite militias and Iraqi government forces burned and looted dozens of villages, abducting at least 11 local residents, in the wake of a U.S.-supported operation against the Islamic State last year, a human rights group has charged in a new report.

Human Rights Watch said that pro-government fighters, after U.S. airstrikes helped them break the extremist group’s siege of the town of Amerli late last summer, left a wake of destruction across at least 30 nearby villages in a manner that was “methodical and driven by revenge.”

Iranian-backed militias and government security forces appeared to have targeted Sunnis, Human Rights Watch found, either because they were suspected of supporting the Islamic State or simply because they came from the same sect as the militant group that controls large parts of Iraq and Syria.

Sarah Margon, Washington director for Human Rights Watch, said the abuses documented in the report should be a warning to the governments of Iraq, Iran, and the United States that new steps are required to ensure that they do not occur after other battles against the Islamic State, such as the one unfolding in the city of Tikrit.

“It’s not just using airstrikes to loosen the grip of ISIS, but it’s what happens in the aftermath,” she said, using another name for the Islamic State. “While the United States may not be on the ground participating in those battles, they have an obligation to think about what’s next.”

Satellite imagery purports to show burned areas in one of the Sunni villages that Human Rights Watch says Iraqi forces ravaged last year. (CNES 2015/ Distribution Airbus DS)

The reported abuses underscore the risks of the Obama administration’s arms-length approach to combatting the Islamic State, which has limited U.S. officials’ ability to direct forces on the ground and ensure they abide by laws of war. Fewer than 3,000 U.S. soldiers are on the ground in Iraq, training and advising Iraqi forces, and are not involved in fighting.

U.S. officials have cited the operation to break the siege of Amerli, where thousands of Shiite Turkmens were stranded without food or water, as one of the most important victories thus far in the international campaign against the Islamic State.

Amerli was seen as an example of the cross-sectarian cooperation that U.S. officials have long hoped to see in Iraq, where in the past government forces have battled Kurdish peshmerga and other powerful militias rather than fighting alongside them.

But even in the early hours after the Amerli operation, residents of nearby Sunni towns expressed fears that they could be targeted by Shiite fighters.

In its report, Human Rights Watch, which used interviews and satellite imagery to document the alleged abuses, said that militiamen, volunteer fighters and security forces looted villages surrounding Amerli, using fire, explosives and heavy machinery to destroy homes and businesses.

The group said it had confirmed destruction in 30 of 35 villages around Amerli. It also documented the abduction of 11 men but said that local residents reported that many others had disappeared.

It is not the first time since Iraq’s battle against the Islamic State erupted last year that Human Rights Watch has reported sectarian abuses. Last fall, the group found that paramilitary fighters and security forces had killed 34 people inside a mosque in Diyala province.

Iraq’s increasing reliance on the militias, funded and armed by Iran, is an uncomfortable reality in Washington, where the Obama administration faces widespread opposition from Republicans in Congress to its negotiations over Tehran’s nuclear program.

U.S. officials, including Army Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, have urged the Iraqi government to ensure that battles against the Islamic State are followed by reconstruction aid and inclusive governance, rather than sectarian reprisals.

In a response to the report, the Iraqi government said that the Islamic State had displaced residents and booby-trapped homes.

Human Rights Watch urged Iraqi Prime Minister Haider al-Abadi to disband the militias, compensate victims and punish those responsible for the abuses. It also called on the Obama administration to ensure an end to such actions before providing additional military assistance or weaponry.

It is unlikely that Abadi, who heads a fragile political alliance, will have the strength to take that step in the near term. Rafid Jaboori, a spokesman for Abadi, said the prime minister, a Shiite, had made clear “there is zero tolerance on human rights violations” and had ordered investigations into recent reports of such abuses. “All Iraqis — Shia, Sunni, Kurds and other smaller communities — are equal,” he said.

Margon said Abadi could articulate and enforce clear guidelines for battlefield conduct, not just for Iraqi forces, but also for all combatants. Otherwise, she said, “the likelihood of it happening [again] is strong.”