Antonio Guterres has again called for an "immediate end to military operations" in southwestern Syria, where Bashar al-Assad regime forces continue their offensive against rebels.
UN Secretary-General Ban Ki-moon's spokesman Stefan Duzaric said in a statement that Antonio Guterres was "deeply concerned" about the Syrian army's attack on the region and "its devastating consequences for civilians".
The UN Secretary-General "recalls that this area of southwestern Syria is subject to a de-escalation agreement reached in July 2017 in Amman between Jordan, Russia and the United States."
He demanded that the "parties that guaranteed" the agreement "keep their commitments".
"All parties must immediately stop carrying out attacks on medical and school facilities" and allow the UN to do so. "To resume humanitarian aid deliveries without delay," he said.
The war in Syria, which entered its eighth year on March 15, has claimed the lives of more than 350.000 people and turned millions more into internally displaced persons and refugees.