The plan, backed by Israel and Western powers, had meant to evacuate 800 people overnight, but only 422 made it because of the increased presence of Islamic State and government roadblocks, the source said.
How did the operation come about?
An Israeli solider hands out water on a bus, during the Syria Civil Defence, also known as the White Helmets, extraction from the Golan Heights, Israel in this still image taken from video, provided by the Israeli Army July 22, 2018.
On June 19, forces of Syria's President Bashar al-Assad launched an Russia-backed offensive to retake Daraa and Quneitra provinces.
Last week the Syrian regime reached a deal through which the rebel groups in the area, defeated and encircled, could surrender.
Israeli forces said it had transferred the rescue workers and their families to a neighbouring country, adding that the operation was "exceptional".
How was it carried out?
Syrian state television said on Sunday an Israeli air strike hit a military post in the city of Misyaf in Syria's Hama province but caused only material damage.
The countries involved in the rescue had determined that the White Helmets were facing an imminent threat.
Jordan, which has closed its borders to refugees, says it had permitted the United Nations bring in 800 rescue workers and their families into the country.More news: Prince Louis’ Official Christening Photos Released By Kensington Palace
Foreign ministry spokesman Mohammed al-Kayed said the kingdom had accepted the members of the Syrian rescue organisation for "purely humanitarian reasons" as their lives had been at risk.
The Syrian government accuses the group of cavorting with terrorists and of staging footage of their operations to garner sympathy and demonize the government.
German Interior Minister Horst Seehofer told Bild newspaper that Germany would take in eight White Helmets members and their families. "We therefore took steps with the aim of affording that protection to as numerous volunteers and their families as possible".
In a statement released early Sunday morning Foreign Affairs Minister Chrystia Freeland pledged Canada's continued support for the White Helmets. "More than 250 White Helmets have been killed in the war since 2013".
The Syrian Observatory for Human Rights said the bombing - 130 airstrikes since Saturday - displaced 20,000 civilians while an estimated 10,000 remain trapped in the area controlled by the militants, with their fate unknown.
A number of those evacuated were from the White Helmets volunteer rescue group, known as the Syrian Civil Defense.
Numbering about 3,000 volunteers, they also carry out essential fix works.
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. His supporters, and his Russian allies, say the volunteers support the rebels and also have links to jihadist groups.
President Assad said it used "humanitarian masks and umbrellas just to implement a certain agenda".