Humanitarian groups and UN agencies are warning of an impending humanitarian catastrophe as the Syrian government troops backed by Russia and Iran prepare to storm the last rebel stronghold in the Idlib province in northwestern Syria.

“There needs to be ways of dealing with this problem that don’t turn the next few months in Idlib into the worst humanitarian catastrophe with the biggest loss of life in the 21st century,” the United Nations’ new humanitarian chief Mark Lowcock told reporters in Geneva.

His remarks came as Syrian troops, supported by Russian air strikes and Iranian troops on the ground, massed around Idlib ahead of an expected onslaught against the largest rebel-held zone left in the country.

Hundreds of thousands of civilians are at immediate threat of displacement and their lives could be endangered by a large scale military offensive on Idlib, CARE International warned Monday.

The area, which is controlled a ragtag alliance of moderate and hardline Islamist groups, including an offshoot of al-Qaeda, is home to 3 million people, two thirds of whom are already in need of aid.

Lowcock acknowledged that “there is a large number of fighters there, including terrorists from proscribed organisations.” But for every fighter “there are 100 civilians, most of them women and children,” he said.

A girl is seen at a makeshift shelter in an underground cave in Idlib, Syria September 3, 2018. Picture taken September 3, 2018. (Khalil Ashawi/REUTERS)

Nearly half of the population has already been displaced from other parts of Syria and lives in difficult conditions, CARE said.

“They might not have a place to go, no refuge from bombs and airstrikes,” Darcy Knoll, a spokesperson for CARE Canada said in a statement. “We could be witnessing a humanitarian catastrophe unlike anything we have seen in Syria since the beginning of the conflict.”

CARE has local partners who operate in this region and have scaled up their assistance, but mass displacement of civilians triggered by a sustained military offensive could put their ability to reach vulnerable populations who are in dire need of assistance at risk, said Knoll.

Officials with the World Food Programme (WFP) said the UN agency and partners are on the ground in Idlib have been delivering monthly food rations for nearly 600,000 people, including families in northern Hama and rural Aleppo through cross-border operations via Turkey and from inside Syria.

Bombardment of northern Hama and South Idlib has already triggered displacement of people to northwest Idlib including Atmeh, Karama, Oah and Dier Hassan among other areas, WFP officials said.

The agency stands ready to reach 850,000 people with emergency food and nutrition for 180,000 children and women.