The group has more than 3,700 women and men in Syria
'We are trapped': White Helmets plead for evacuation from Syria
A senior member of the Syrian "White Helmet" rescue workers called on the United Nations to save his colleagues trapped in the southwest by advancing government forces.
Israel and Western powers helped evacuate 422 White Helmets and their families from Syria into Jordan last week but others were unable to make it out because of government checkpoints and the expansion of ISIS in the area.
Forces loyal to Syrian President Bashar Al Assad, backed by the Russian military, have captured most of the southern province of Deraa in an offensive that began in June.
"We want the UN or any international agency to remove the White Helmets volunteers from Deraa to Idlib so we can continue to work in the north of Syria" Majd Khalaf, one of the founders of the White Helmets, said on Thursday.
"It is so hard when White Helmets have to leave people behind - and they also have to start their lives over," he told the Thomson Reuters Foundation by phone from Istanbul, Turkey.
He declined to say how many White Helmets were still at risk in the area, but said that the group has more than 3,700 women and men in Syria and that more than 200 volunteers have been killed in the seven-year civil war.
The group, known officially as Syria Civil Defence, has been widely hailed in the West and credited with saving thousands of people in rebel-held areas during years of bombing attacks by Damascus and its allies.
Its volunteers, famed for their white helmets, say they are neutral. But President Al Assad and his backers, including Russia, have dismissed them as Western-sponsored propaganda tools and proxies of insurgents.
The Syrian government on Monday condemned last week's evacuation as a "criminal operation" undertaken by "Israel and its tools".
Government forces backed by Russian air power have swept through southwestern Syria in the last month, in one of the swiftest campaigns of a war estimated to have killed hundreds of thousands of people and displaced 11 million.
"After the control of the regime on all borders and the whole area, we are trapped and cannot move," one White Helmet in Deraa, who declined to give his name, said via WhatsApp, adding that he fears being arrested.
Raed Al Saleh, director of the White Helmets, said his volunteers were "helpless" as they are a civilian organisation.
"Unfortunately we wish we could stay in these areas, but it is not in our hands," he said by phone from Turkey.
"We are asking for their evacuation to protect them."