The Syrian government has condemned the evacuation over the weekend of the White Helmets civil defence group from a war zone in the south of the country.
Damascus described the move, carried out by Israel, as a "criminal operation" by "Israel and its tools".
Some 422 volunteers and family members were taken to Jordan via the Israeli-occupied Golan Heights.
It was feared that they would be persecuted by advancing government forces in southern Syria.
Responding to the move on Monday, Syria's foreign ministry said that "words of condemnation are not enough to denounce this despicable act".
It added that the White Helmets supported "terrorists" and that the world had been warned of the group's "dangers", according to Syria's state news agency Sana.
Syrian President Bashar al-Assad's administration regards the White Helmets as agents of Western powers. His supporters, and his Russian allies, say the volunteers support the rebels and also have links to jihadist groups.
But Mr Assad's opponents see them as heroes for their rescue work in bombed, rebel-held cities.
The White Helmets describe themselves as a volunteer workforce that acts to save people in Syria's war zones.
How and why was the operation carried out?
The Israel Defense Forces (IDF) said they were acting on a request from the US, the UK and other European nations.
The White Helmets had become trapped in an area of south-western Syria near the border with the Golan Heights after an offensive by the Syrian military.
The offensive, which began in June, has seen a number of agreements that have led to the evacuation of rebel forces from the Deraa and Quneitra areas to regions further north.
The White Helmets operate only in rebel-held areas, although they say they are non-partisan.
The evacuees were driven to the border with the Golan Heights and taken on from there by Israeli troops to Jordan.
The plan had been to evacuate 800 White Helmets and their families, but only 422 made it.
The BBC's Mark Lowen said that others had been hemmed in by the expansion of the Islamic State group into pockets of south-west Syria and, as this was a one-off operation, fears remain for the fate of those left behind.
Those successfully evacuated included about 100 White Helmets, with the rest family members.
Who are the White Helmets?
Their official name is the Syrian Civil Defence, which began in early 2013 as an organisation of volunteers from all walks of life, including electricians and builders.
Its main task soon became to rescue civilians in war zones in the immediate aftermath of air strikes, and it says its volunteers have saved the lives of more than 100,000 people during the civil war.
Numbering about 3,000 volunteers, they also carry out essential repair works. Some 200 members have been killed.
The White Helmets have gained worldwide praise, were nominated for the 2016 Nobel Peace Prize and were the subject of a Netflix documentary and BBC Panorama programme.
But Syria's government and its ally Russia have accused the group of links to jihadist groups.
President Assad said it used "humanitarian masks and umbrellas just to implement a certain agenda".
The group has been financed by public donations, as well as funding from foreign governments.