German Chancellor Angela Merkel on Thursday urged Russia and Iran to rein in Syrian forces’ offensive against a rebel-held suburb of Damascus, calling the attacks a massacre.

The comments come hours before a possible vote by the United Nations Security Council on a resolution for a 30-day cease-fire in Syria to allow for the delivery of humanitarian aid, an end to sieges and attacks against civilians in Syria.

According to the so-called White Helmets, at least 250 people have been killed in recent days in Eastern Ghouta, a suburb of the capital that is home to about 400,000 people and has been under siege for five years. The regime of Syrian President Bashar al-Assad, backed by Russian warplanes, is continuing its battle to restore control of Syria after a seven-year civil war.

“The regime is not fighting against terrorists, but against its own people, killing children, destroying hospitals, and this is a massacre to be condemned,” Ms. Merkel said in Germany’s parliament.

She said that Iran and Russia, the Assad regime’s main backers, have a particular responsibility for the situation. Moscow and Damascus deny targeting civilians and civilian infrastructure and say they are focused only on rebels fighting the government.