WASHINGTON — Pentagon officials said Tuesday that they are investigating claims anti-Islamic State coalition airstrikes killed dozens of Syrian civilians near a city where U.S.-backed rebels were attacking the terrorist group.

The Islamic State group controls Tokhar and Hoshariyeh, two northern Syrian villages where at least 56 civilians were killed in a series of strikes early Tuesday morning, according to the Syrian Observatory for Human Rights, a Great Britain-based activist organization. Another activist group,the Turkey-based Syrian Institute for Justice said Tuesday that more than 85 civilians had been killed in four aerial attacks on the towns.

The Defense Department was conducting a “credibility assessment” of the claims, according to Pentagon officials, though they did not provide additional information.

The claims came just days after the U.S.-backed Syrian Democratic Forces captured the Islamic State group’s headquarters in Manbij. Syrian Democratic Forces, which are mostly Kurdish, have worked for six weeks to capture the city, which serves as the terrorist group’s last supply route connecting its capital in Raqqa to Turkey and the outside world. SDF, which the United States has said includes a sizable force of Arabs native to the Manbij area, captured a hospital in the western part of the city Sunday that served as the Islamic State’s command center and housing for at least some of its fighters.

Capturing the hospital “posed a significant challenge,” said Matthew Allen, a DOD spokesman. Islamic State militants had heavily fortified the structure, but SDF and coalition commanders were limited in the amount of force that they could use against the building because they intended to keep it in tact.

SDF have worked for several weeks to liberate the building, which they hope to quickly return to civilian health-worker control. Allen said it was in decent shape, and SDF were preparing to protect the structure from counterattacks.

The Islamic State group has held Manbij since January 2014. It has served as a key smuggling route for supplies and foreign fighters.

SDF encircled the city last week and have been working along four fronts to methodically clear the city of Islamic State fighters. Those fighters have mounted a strong resistance at the city’s center, but SDF are “maintaining its momentum with support from coalition strikes,” according to a U.S. Central Command statement.

At least 18 strikes in and around Manbij have targeted the Islamic State group since Monday, according to the U.S.-led Operation Inherent Resolve coalition. Those strikes destroyed 13 Islamic State group fighting positions, seven vehicles and two vehicle-borne improvised explosive devices. The coalition has conducted more than 450 total strikes near Manbij in the last two years.

Pentagon officials said the coalition carefully selects its targets to “avoid or minimize civilian casualties or collateral damage.”

Central Command reported in May that the DOD’s airstrikes in Iraq and Syria had killed 41 civilians since beginning Operation Inherent Resolve in August 2014.

dickstein.corey@stripes.com

Twitter: @CDicksteinDC

