The Trump administration is accusing the Syrian government carrying out mass killings of thousands of prisoners and burning the dead bodies in a large crematorium outside the capital. The State Department says about 50 detainees a day are being hanged at Saydnaya (Said-nay-ah) military prison, about 45 minutes from Damascus. It says the crematorium is being used to hide evidence of the extent of the killings. The department is releasing newly declassified photographs showing what it says is a building in the prison complex that has been modified to support the crematorium. In presenting the photographs, the top U.S. diplomat for the Middle East, Stu Jones, said Monday that Syrian President Bashar Assad’s government “has sunk to a new level of depravity” with the support of Russia and Iran.

Meanwhile, air raids on an Islamic State-held village and town in Syria have killed at least 32 civilians over the past two days, activists said Monday, underscoring the risk for hundreds of thousands of residents trapped in areas under the militant group’s control ahead of the looming battle for Raqqa.

The U.N. envoy for Syria meanwhile insisted that the latest round of peace talks between the government and the opposition in Geneva are serious, after President Bashar Assad said last week that they were just for show.

Staffan de Mistura assured reporters that the government delegation attending the talks is “here to work.” The talks are scheduled to begin Tuesday and last around four days.

The envoy declined to comment on Assad’s remarks, aired by Belarus ONT television on Thursday. The Syrian leader said “nothing substantial” would come from the talks and that they were “merely a meeting for the media.”

The delegations aren’t expected to meet face-to-face, and de Mistura has called for reduced media involvement to foster a more “businesslike” atmosphere.

It was not immediately clear who was behind the strikes on the village of Akayrshi on Sunday and the town of Boukamal on the Syrian-Iraqi border Monday. Activists blamed the U.S.-led coalition, which responded to an Associated Press query by saying it would look into the reports.

The coalition has come under increasing scrutiny by monitoring groups regarding civilian casualties in the fight against the Islamic State group in both Iraq and Syria. The Pentagon acknowledged late last month that at least 352 civilians have been killed by coalition strikes in the two countries since the start of the air campaign against IS in 2014.

However, activists and monitoring groups say the number is much higher. Access is restricted to IS-held areas, and details are hard to come by.

The raid on Boukamal took place around 3 a.m., according to the activist-run Justice for Life, with fighter jets striking a mosque and surrounding houses. Omar Abu Laila, of the activist-run Deir Ezzor 24, said the airstrikes destroyed 15 homes and killed at least 20 civilians who had fled from other areas in Iraq and Syria.

The Britain-based Syrian Observatory for Human Rights said 23 civilians were killed, with the toll likely to rise. Observatory director Rami Abdurrahman says IS fighters were also killed.

The Observatory said 12 women were killed in the strikes on the village of Akayrshi, while the activist-run Raqqa is Being Slaughtered Silently said the strikes hit a convoy of farm workers, killing 22 people.

The IS-run Aamaq news agency claimed 22 women were killed and eight wounded in a drone strike on a bus in Akayrshi, which is about 16 kilometers (10 miles) from Raqqa, the group’s self-styled capital. It said another 25 civilians were killed in Boukamal.

U.S.-backed and Kurdish-led Syrian forces are advancing on Raqqa after capturing several nearby towns and villages from the extremists.

The Trump administration last week authorized the Pentagon to supply the force with heavy weapons for the Raqqa campaign, rankling Turkey, which says the fighters are affiliated with Kurdish insurgents operating within its own borders.

President Vladimir Putin praised the Syrian Kurdish force as “one of the most efficient units” battling IS and said Moscow has “working contacts” with them, but he said his country is not planning to provide arms. Putin said the Kurds “have other sources of obtaining the weapons.”

Russia has been waging an air campaign to support Assad’s forces since 2015.

In Damascus, governor Beshr al-Sabban said Monday that a northeastern neighborhood of Damascus is now completely under government control after carrying out the second and last phase of a truce agreement in the area.

Hundreds of rebels and their families left Qaboun on Sunday and Monday, headed toward rebel-held areas, bringing all parts of the capital under the control of President Bashar Assad’s forces for the first time since 2012.

The evacuations came a day after government forces and their allies captured most of the area from insurgents who had maintained a presence in the northeastern neighborhood for four years. The departures from Qaboun come days after hundreds of opposition fighters were evacuated from the nearby neighborhoods of Barzeh and Tishrin.

State-run news agency SANA quoted al-Sabban as saying that military units were combing the neighborhood to dismantle explosives and mines.