Civilians fleeing the militant Islamic State (IS) group's two remaining Syrian strongholds face “terrible, terrible conditions” in dozens of poorly-equipped informal camps, the International Committee of the Red Cross (ICRC) said on Monday.

IS is under pressure in the remaining areas it holds in Syria, with a US-backed force battling to oust the militants from its bastion Raqa, and regime troops closing in on terrorist-held parts of Deir Ezzor.

However, the fighting has displaced tens of thousands of people, with many taking refuge in camps in the provinces of Raqa and neighbouring Hasakeh.

Ingy Sedky, a Damascus-based spokeswoman for the ICRC, said more than 40 camps, each hosting anywhere between 2,000 and 10,000 people, had been set up in often-remote areas in the two provinces.

“These tents are literally in the middle of the desert. You have snakes and scorpions that are a daily threat for people,” she told AFP after visiting the camps with an ICRC team to assess conditions.

“Fifty per cent of the people inside these camps are children. They are living in terrible, terrible conditions because of the heat. It can be 50 degrees Celsius during the day.”

She said many camps lacked even the most basic items, including tents, with new arrivals sleeping in the open for up to 10 days while waiting for shelter.

“There is one camp called Arisha in Hasakeh governorate. The camp itself used to be a petroleum refinery, so you see children playing in toxic waste, drinking and bathing in contaminated water,” she said.

“Most of the camps don't have doctors on site ... They don't even have bandages, even the simplest things are not available.”

She claimed that an estimated 70,000 people were living in such camps, which are often in hard-to-reach locations, complicating aid provision.

The US-backed Syrian Democratic Forces, an alliance of Kurdish and Arab fighters, began an operation to capture Raqa from IS last year, and now holds much of the province and over half of Raqa city.

Government forces, meanwhile, are approaching IS-held territory in the eastern province of Deir Ezzor from two axes, and are expected to launch an operation to break the militant group's years-long siege of regime-held parts of the provincial capital.

Sedky said there has been an uptick in people fleeing Deir Ezzor.

“Every day and night there are people, tens at least, who arrive,” she said.

Sedky said ICRC would be working to improve water access and medical support in the camps.

“The first priority is water. It is essential that people have clean water, because you can see already this is creating a lot of diseases [including chronic diarrhoea]," she said.

“The basic medicines even are not available, let alone what you would need for people with chronic diseases. “