Syrian government forces have been bombarding southern and eastern parts of Idlib province, the last rebel stronghold in the war-torn country since late November.
Since the eruption of the bloody civil war in Syria in 2011, the Assad regime and Russian Federation attacks killed almost 1,000 humanitarian workers, according to a Syrian human rights watchdog on Wednesday.
A statement from a representative of UN Secretary General Antonio Guterres said he was "deeply concerned" about the escalation and called for an immediate cessation of hostilities.
"The continued silence of (the) global community is seen as an open invitation for the Syrian regime and the Russians to continue to challenge worldwide humanitarian law, act outside the law and commit more crimes against civilians", the group said.
The site of the attack was strewn with destroyed tents and smoking debris, said an AFP correspondent there. I say it again: "if you try to frame our operation there as an invasion, our task is simple: "we will open the doors and send 3.6 million migrants to you", Erdogan said.
The war in Syria, now approaching its ninth year, has devastated much of the country.
Residents of the southern Idlib town flooded out of the area fearing violent clashes, an AFP correspondent there said.
A total of 979 humanitarian workers, 882 of which were killed by the Assad regime and 97 by Russian Federation in March 2011-December 2019, according to a report by the Syrian Network for Human Rights (SNHR).
Under the cover of air strikes and heavy shelling, Syrian regime forces have been pushing into the northwestern province of Idlib toward a rebel-held town, Maaret al Numan.
It pledged to continue its push until it recaptures all of Idlib, calling on civilians to exit areas under jihadist control. Many have been heading toward the Turkish border for safety.
He added: "If the violence towards the people of Idlib does not stop, this number will increase even more".
The government of Syrian President Bashar al-Assad has repeatedly promised to recover the area, and the bombing has continued despite a ceasefire announced in August. It's also home to three million civilians, and the United Nations has warned of the growing risk of a humanitarian catastrophe along the Turkish border. For its part, France has released additional emergency assistance of €5.27 million for the civilian population of north-west Syria, via the UN Cross-Border Humanitarian Fund based in Gaziantep.