A general view of the refugee camp near Atimah village, Idlib province, Syria, Sept. 11 ,2018. (REUTERS Photo)

UNITED NATIONS, Sept. 11 (Xinhua) -- UN Secretary-General Antonio Guterres said Tuesday that it is "absolutely essential" to avoid a full-scale attack on Syria's Idlib, the last major rebel stronghold in the country.

"This (A full-scale attack) would unleash a humanitarian nightmare unlike any seen in the blood-soaked Syrian conflict," said the UN chief in a press encounter at UN Headquarters in New York.

Almost half of Idlib's population of 2.9 million people had gone there to seek refuge from conflict elsewhere in Syria, including nearly 1 million children. Their lives have been upended and they have nowhere to go, he said.

"Idlib is the last so-called 'de-escalation zone' in Syria. It must not be transformed into a blood bath."

Guterres reminded parties to the conflict of their obligations under international law to protect civilians.

"I understand that the present situation in Idlib is not sustainable and the presence of terrorist groups cannot be tolerated. But fighting terrorism does not absolve warring parties of their core obligations under international law," he said. "I make a clear appeal to all parties directly and indirectly involved -- and in particular the three guarantors of the de-escalation zone, namely Iran, Russia and Turkey: Spare no effort to find solutions that protect civilians. Preserve basic services such as hospitals. Ensure full respect for international humanitarian law."

It is important that the parties -- especially the three guarantors of the Astana process -- find a way in which it is possible to isolate terrorist groups and it is possible to create a situation in which civilians will not be the price paid to solve the problem of Idlib, he said.

The three guarantors bear a particular responsibility since they have their own posts around the situation in Idlib and they have negotiated for a long time the de-escalation zones and different other forms and arrangements, said the UN chief.

It also goes without saying that in the 21st century any use of chemical weapons is totally unacceptable, said Guterres. "Beyond the immediate human toll, such use would lead to a situation spiraling out of control," he warned.

He asked for peace-making efforts, particularly within the framework of the UN-led Geneva process.

There is an urgent need to make greater progress in the Geneva process, and in particular the creation of a constitutional committee as part of the overall political package, he said. "There is no military solution to the conflict. The solution must be political."

"We have a collective responsibility to protect people who have already suffered too much," he said.