GENEVA: UN officials warned Thursday that the collapse of a ceasefire in Syria's Idlib province had triggered "total panic" and threatened the lives of millions.
The Syrian regime this week declared a short truce in the country's north-west was finished and fighting resumed immediately.
The United Nations has raised specific alarm about the risks of a massive government offensive in the area because Idlib has for several years served as a reception zone for those escaping government advances elsewhere in the country.
The UN's humanitarian chief for Syria, Panos Moumtzis said a possible government offensive in the area was "like playing with fire".
"These people don't know where to go," he said, stressing that there is no other opposition stronghold where people can flee if Idlib confronts a full assault by President Bashar Al-Assad's forces. "A total panic has resumed again," he added.
He spoke after a meeting in Geneva that including envoys from Syrian ally Russia, which has reportedly hit southern Idlib with airstrikes this week.
"It is like playing with fire at the moment and we worry about it coming out of control," Moumtzis said.
Najat Rochdi, a senior humanitarian adviser to to UN Special Envoy for Syria Geir Pedersen said more than 500 civilians were killed in the region since late April.
"Humanitarian actors are increasingly concerned by statements suggesting a possible military intervention, which would have severe humanitarian consequences in an area that has already witnessed years of military activity, displacement, droughts and floods," she said.
The jihadist-run bastion of Idlib, the last major opposition stronghold in Syria, is currently home to about three million people.
The UN has said that an estimated 400,000 people have been displaced within Idlib over the last 100 days.
Contingencies are in place for up to 900,000 displacements but there were no plans for managing an offensive that affected Idlib's entire population, Moumtzis said.
"What is the... plan for the three million people there?" he said. "That is a question we haven't got an answer for".
Hayat Tahrir al-Sham (HTS), a jihadist group led by Syria's former Al-Qaeda affiliate, has controlled most of Idlib province since January.
A truce that started last Friday was supposed to protect civilians in the region, halting three months of deadly regime and Russian bombardment.
But HTS on Saturday refused to comply with a key condition to that truce, vowing it would never withdraw from a planned buffer zone around the area.
On Monday, the government declared the ceasefire over, accusing its opponents of attacking civilian areas and bombarding a Russian air base.
British foreign minister Dominic Raab slammed Al-Assad for resuming military operations.
"Appalled by situation in Idlib and how Assad backed by Russia revoked a 'conditional' ceasefire just days after announcing it - a repeated pattern of behaviour," Raab said on Twitter.
"Attacks on civilian targets are a violation of international humanitarian law – this must stop."