*UN agencies warn of the worst humanitarian tragedy of the 21st century

United Nations Secretary-General Antonio Guterres on Tuesday appealed to Russia, Iran and Turkey to "spare no effort to find solutions that protect civilians" in Syria's Idlib and said it was "absolutely essential" a full-scale battle was avoided.

"This would unleash a humanitarian nightmare unlike any seen in the blood-soaked Syrian conflict," he told reporters
An estimated 3mn people live in Idlib - the last major stronghold of active opposition to President Bashar al-Assad. The UN has described it as a "dumping ground" for people evacuated and displaced from elsewhere in Syria during the seven-year war.
Assad has vowed to retake the region, backed by his Russian and Iranian allies. Syrian government and Russian warplanes began air strikes in Idlib last week in a possible prelude to a full-scale offensive. They say they are targeting terrorist groups.
Senior officials from Russia, Iran and Turkey met with UN Syria envoy Staffan de Mistura in Geneva Tuesday. The presidents of Turkey, Iran and Russia met in Tehran on Friday but failed to agree on a ceasefire in Idlib.
A full-scale military offensive on Idlib risks creating the worst humanitarian tragedy of the 21st century, UN aid agencies have said, amid concerns that a severe funding shortfall threatens the most vulnerable victims of the conflict.
"We as humanitarian advocates must raise our voice," said Jens Laerke from the Office for the Coordination of Humanitarian Affairs (OCHA). "We are saying that this has the potential to be the worst crisis - humanitarian crisis - in the 21st century, because that is frankly what it looks like, if it goes ahead with a full-scale military operation."
Since September 4 , an uptick in violence has killed scores of civilians and displaced more than 30,000 people, Laerke said.
Regional Humanitarian Coordinator for the Syria Crisis Panos Moumtzis noted that aerial and ground-based bombardment had struck northern rural Hama governorate and southern rural Idlib, and had been accompanied by an increase in retaliatory rocket and mortar attacks.
The resulting impact on civilians has been dramatic, Laerke said, his concerns echoing those of UN Emergency Relief Coordinator Mark Lowcock, who a day earlier had issued a warning about a military escalation in Idlib, after a recent meeting with Syria government officials in the country's capital.
"As the Emergency Relief Coordinator mentioned, he was recently in Damascus", noted Laerke, adding that the Syrian Government had indicated it would pursue a military solution "which is very, very scary from a humanitarian perspective."
"They have this capacity to kill and destroy," Laerke said. "We have seen it in use before, and we strongly advise that it does not happen in this enclosed area, where the population has, I think, almost doubled by the influx of evacuees and IDPs from other parts of the country."
In the space of less than a week, four hospitals have been hit in southern Idlib and neighbouring Hama governorate.
This is contrary to international humanitarian law, the OCHA spokesperson said, adding that one of the hospitals was also in a protected "deconfliction zone", whose coordinates had been given to the warring parties to spare it from attack.
"Our fear as humanitarians is that the worst may be ahead of us," the statement from Panos Moumtzis read. "The safety and protection of some 2.9mn civilians residing in Idlib and surrounding areas is at risk."