WASHINGTON — The United States accused Syria on Monday of executing thousands of imprisoned political opponents and burning their bodies in a crematorium to hide the evidence, testing the Trump administration’s willingness to respond to atrocities, other than chemical weapons attacks, that it blames on President Bashar Assad’s government.

The allegation of mass killings came as President Donald Trump weighs options in Syria, where the U.S. launched cruise missiles on a government air base last month after accusing Assad’s military of killing scores of civilians with a sarin-like nerve agent. Trump on Monday kicked off a week of meetings with Middle East leaders, sitting down with the crown prince of Abu Dhabi a day before he hosts Turkey’s president. Trump flies to Saudi Arabia later this week.

All are governments that have pressed the United States over six years of civil war in Syria to intervene more forcefully. Trump had backed away from President Barack Obama’s calls for regime change in the Arab country, with the new president’s officials pointedly saying leadership questions should be left to Syria’s citizens, until his intervention last month. His administration now says Assad cannot bring long-term stability to Syria.

In its latest accusations of Syrian abuses, the State Department said it believed about 50 detainees each day are being hanged at Saydnaya military prison, about 45 minutes north of Damascus. Many of the bodies are then burned in the crematorium “to cover up the extent of mass murders taking place,” said Stuart Jones, the top U.S. diplomat for the Middle East, accusing Assad’s government of sinking “to a new level of depravity.”

The department released commercial satellite photographs showing what it described as a building in the prison complex that was modified to support the crematorium. The photographs, taken over the course of several years, beginning in 2013, do not prove the building is a crematorium, but show construction consistent with such use.