The White Helmets, the collective of Syrian volunteers who rescue civilians from under the rubble of destroyed buildings, has said hundreds of its members and their families fled Syria on Saturday due to fears of reprisals by the government of Bashar al-Assad.

In its first statement since the dramatic rescue operation, the group said it had suffered systematic attacks by regime forces, and that surrender deals negotiated with local rebels did not allow for the evacuation of humanitarian workers.

A total of 422 people – 98 rescue workers plus their families – were taken to Jordan through the Israeli-occupied Golan Heights as Syrian regime forces closed in during the final hours of an offensive that reclaimed most of the provinces of Deraa and Quneitra.

“As Syrians who love their country, our hearts are broken because we were forced to leave it, but that was the only option for our trapped volunteers who were facing the danger of detention or death at the hands of the Syrian regime and its Russian allies,” the statement said.

The volunteers from the White Helmets, also known as the Syrian Civil Defence, are now in Jordan where they are awaiting resettlement. The country agreed to take them in as part of an operation backed by the US, UK, Canada and Germany, and facilitated by Israel.

The Assad regime, backed by Russian airstrikes, reclaimed much of southern Syria in a swift offensive that began in mid-June. The government’s victory in the birthplace of the Syrian uprising was cemented by surrender deals in which local rebels agreed to forced exile in the north or to resolving their status and remaining in their homes.

The White Helmets, who have rescued thousands of civilians and who have lost 251 volunteers, often to targeted regime attacks, have long been the target of propaganda campaigns on social media smearing them as extremists or agents of foreign powers and accusing them of staging attacks.

The Syrian government denounced the rescue of the volunteers as a “criminal process” that involved the smuggling of terrorists.

A senior White Helmets official said the organisation’s volunteers had been threatened with arrest, barring them from seeking refuge in the country’s north with others who signed up to the surrender deals.

“There were a lot of threats from the regime to detain civil defence members who want to leave for the north,” said Mounir Mustafa, the organisation’s deputy chief. “There was a grave danger on those individuals.”

There are still more than 3,700 White Helmets volunteers in various parts of Syria.

More than a dozen demonstrated on Tuesday in rebel-held districts of Deraa to demand safe passage out. Hundreds more remain trapped in the war-ravaged south, fearing reprisals from approaching regime troops.