The United States on Tuesday condemned the forced surrender of one of the last rebel-held enclaves in Syria and accused Syrian government forces of using a U.N.-backed cease-fire to accomplish it.

Nikki Haley, the U.S. ambassador to the United Nations, blamed Russia for supporting Syrian President Bashar Assad and playing a “central role in the bombing of Syrian civilians into submission.”

Haley, speaking at a special session of the U.N. Security Council, also lashed out at her fellow members of the organization, saying they had failed to call out Russia and Syria’s other key ally, Iran. She was reacting to reports that the enclave of eastern Ghouta, near Damascus, had all but fallen to government forces, and thousands of civilians were being forced to flee.

“Siege. Starve. And surrender,” she said. “This is the awful, unceasing rhythm of the Syrian war. As we meet here today, the third step — surrender — is taking place in eastern Ghouta.”