Drug dealer "Marai al-Ramthan, his wife and six children were killed in a Jordanian air force strike" in the eastern countryside of the Sweida province, near the Syrian-Jordanian border, the Britain-based Syrian Observatory for Human Rights said.

"Ramthan is considered to be the most prominent drug trafficker in the region, and the number one smuggler of drugs, including captagon, into Jordan", said the Observatory, which relies on a wide network of sources inside Syria.

When asked about the strike, Jordanian Foreign Minister Ayman Safadi told reporters: "When we take any steps to protect our national security... we will announce them at the appropriate time".

"Drugs... are a great threat to the kingdom, the region and the world as smuggling operations soar," Safadi said.

An AFP investigation in November found that Syria has become a narco state, with the $10 billion captagon industry dwarfing all other exports and funding both Assad and many of his enemies.

The main destinations are oil-rich Gulf countries, but Jordan has also become a transit route for trade in the amphetamine-type stimulant that has been sweeping the Middle East for years.

An activist in Sweida province with knowledge of the local drug trade told AFP that "we expect to see a noticeable impact on smuggling operations from Sweida after the strike."

"No one could smuggle anything across the border without Ramthan's knowledge," he said, requesting anonymity for his own security.

Some traffickers in the area have fled their homes following the strike, the activist added.

The rare attack comes on the heels of a May 1 meeting of several Arab foreign ministers in Amman in which Damascus had agreed to "enhance cooperation" with countries "affected by drug trafficking and smuggling across the Syrian border", a Jordanian foreign ministry statement said.

It added Syria would work with neighbours Jordan and Iraq to identify sources of drug production and smuggling, and seek "steps to end smuggling operations".

Jordan's army had said last year drug trafficking from Syria into Jordan had become "organised", with smugglers stepping up operations and using sophisticated equipment including drones, warning of a shoot-to-kill policy.

During the first two months of 2022, the army said Jordanian forces had killed 30 smugglers and foiled attempts to smuggle 16 million captagon pills from Syria -- surpassing the entire volume seized throughout 2021.

Jordan has previously launched strikes targeting drug smugglers in Syria, some dating back to 2014.

On Sunday, the Arab League welcomed Syria back into the bloc after a more than a decade-long suspension, securing President Bashar al-Assad's return to the Arab fold after years of isolation.