UNITED NATIONS, Feb. 14 (Xinhua) -- The UN special envoy for Syria on Wednesday stressed the need for the immediate de-escalation of violence in Syria.

"This is as violent and worrying and dangerous a moment as any that I have seen in my time as special envoy," Staffan de Mistura told the Security Council. "I strongly reiterate the appeal of the (UN) secretary-general to all concerned in Syria and the region and beyond to de-escalate immediately and unconditionally, and urge all stakeholders ... to use their influence to help reduce violence."

There has been a gradual return to back-and-forth competition over territory in Idlib and Hama provinces, and heavy and sustained airstrikes across the northwest and in besieged eastern Ghouta, said de Mistura.

Civilians has been killed on a horrific scale and strikes have continued to hit hospitals, schools and markets. Reports suggest that more than 1,000 civilians lost their lives in the first week of February alone, he said.

There have been several allegations of chemical weapons attacks in Ghouta and Idlib, and in the Afrin district on the border with Turkey, he said. Although those allegations cannot be verified as there is no independent investigation, they are extremely worrisome, said de Mistura.

At least 320,000 people have been displaced due to fighting in Idlib in just two months, an area that is already hosting over 1.2 million internally displaced people, he said.

The conflict is also further spilling over Syria's borders in more than one direction and there have been increased military intervention from multiple sources, he said.

The last several weeks have seen a new cross-border conflict in Afrin involving Turkish troops "with yet no clear end in sight," said the special envoy.

There are reports of exchanges of fire between Turkish and Syrian government forces in Idlib, and between the U.S.-led coalition and pro-Syrian government forces in the Euphrates valley, with major loss of life, he said.

"We have seen Russian and Turkish aircraft shot down over northern Syria. And now over the last weekend, there have been Israeli reports of an Iranian drone entering Israeli airspace -- reports denied by Iran; Israeli jets striking targets inside Syria reportedly from the Lebanese airspace; an Israeli jet reportedly shot down by Syrian government anti-aircraft fire; and what Israel calls large-scale strikes against the Syrian Aerial Defense System and Iranian targets."

The escalation of violence has deprived Syrians of the humanitarian assistance they need, said Mistura.

There has not been a single UN humanitarian convoy to any besieged area since the end of November -- two and half months till now, he noted.

De Mistura asked for international efforts to ensure immediate and unfettered humanitarian access to besieged and hard-to-reach areas in particular.

A series of urgent consultations to that end are under way in Geneva -- without concrete results so far, he said.

"We urgently need genuine de-escalation to protect civilians, evacuate the sick and wounded, and allow humanitarian aid to reach nearly 3 million people in besieged and hard-to-reach areas."