"These reports are extremely troubling, and make a mockery of the so-called "de-escalation zones" meant to protect civilians from such bombardment", said Paulo Pinheiro, chair of the Commission.
"Civilians and children being massacred and the world is still silent", Rami Abdel Rahman, head of the Britain-based Syrian Observatory for Human Rights, said. The Observatory said 47 people had been killed, while the Civil Defence put the death toll at 45.
Meanwhile, the UN-mandated Independent International Commission of Inquiry on Syria expressed deep concern over the further escalation of violence in Idlib governorate and in eastern Ghouta.
United Nations officials in Syria called for fighting to stop to enable aid deliveries and the evacuation of sick and wounded, listing seven areas of concern including northern Syria's Kurdish-led Afrin region, being targeted by a Turkish offensive.
Airstrikes and shelling of areas held by anti-government armed groups has compounded a three-year siege in which almost 400,000 civilians - including children - have had little access to basic assistance, including food, medicines and life-saving health assistance.
Though Mr Al Assad appears to have survived the insurgency, his forces continue to bomb and besiege opposition pockets around the country.
"The agreed inter-agency bi-monthly plan to reach besieged and hard-to-reach areas is paralyzed due to access restrictions or lack of agreement concerning locations, supplies and number of beneficiaries", the statement said.More news: USA Gymnastics doctor Nassar receives additional 125yr prison sentence
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In a broadcast with the word "urgent" superimposed, it said at least 30 people had been killed and that airstrikes are still underway in the Ghouta. It said one of its workers was also killed by an airstrike while responding to a call for rescue in the area.
Turkish President Recep Tayyip Erdoğan on Tuesday warned the United States to withdraw any American forces from the Syrian town of Manbij, vowing that Turkish troops would expand a cross-border military operation to the key strategic hub.
Two more Turkish soldiers were killed over the past weekend during combat operations in Afrin, a Kurdish control city/region in northern Syria. An offensive by Ankara to rout USA -backed Syrian Kurdish fighters from the northern enclave of Afrin is now in its third week.
Turkey began deploying forces in an observer role to the rebel-held Idlib in October as part of a "de-escalation" agreement with Iran and Russian Federation to stabilize the lines of conflict in the war-torn country.
"We implore the worldwide community to speak with one voice, taking every opportunity to publicly pressure the Assad regime, and its supporters, to cease its use of chemical weapons", spokeswoman Heather Nauert said in a statement Monday night.
That deal largely collapsed in December when the Syrian army along with Iran-backed militias and heavy Russian air power launched a major offensive to take territory in Idlib province and surrounding areas.