The report by the Britain-based Syrian Observatory for Human Rights came after Jordan's military said that several "drug traffickers" had been killed or wounded in clashes with Jordanian border guards at the northern frontier with Syria since Monday.

"Four people were killed, including a woman and two children, in air strikes carried out last night by Jordanian warplanes that targeted a farm in the border province of Sweida," the Observatory said.

The strikes targeted areas along the Jordan-Syria border "where drug traffickers carry out smuggling operations", said the Observatory, which relies on a network of sources inside Syria for its reports.

A fifth person was killed in a separate strike on another farm which belongs to Faisal al-Saadi, a trafficker said to be close to Lebanon's powerful Hezbollah movement and to the Syrian government's security department, the monitor said.

According to the Jordanian army, "several traffickers have been killed or wounded during clashes with Jordanian border guards and armed groups at the northern frontier since dawn on Monday".

A statement said that a number of drug traffickers had been arrested by Jordanian authorities, including nine Syrian citizens, and large quantities of drugs and weapons seized.

Several Jordanian border guards were also wounded in the clashes, the army statement added.

Jordanian security forces have tightened border controls in recent years and occasionally announce thwarted drugs and weapons smuggling attempts from Syria.

One of the main drugs smuggled is the amphetamine-like stimulant captagon, for which there is huge demand in the oil-rich Gulf.

In July, a newly-established forum to combat drug smuggling from war-ravaged Syria held its first meeting in the Jordanian capital, Amman.

It was agreed during talks between Jordanian Foreign Minister Ayman Safadi and Syrian President Bashar al-Assad, amid regional concerns over an influx of captagon.

There has been increasing regional engagement with Assad's government since its readmission to the Arab League in May, ending more than a decade of isolation since civil war erupted in Syria in 2011.