Others also carrying drugs fled back into Syria during the attempted crossing, one of a growing number of such incidents over the past year, many involving firefights, which have prompted the army to toughen its rules of engagement with smugglers.

Several others among the smugglers, who were "supported by other armed groups", were wounded, the army said in a statement.

It did not specify where along the border the incursion took place.

Many smugglers have favoured Jordan's main border crossing to the Gulf region, where the army has found drugs, most commonly an amphetamine known as Captagon, hidden in Syrian trucks.

Jordanian officials say Lebanon's Iran-backed Hezbollah group and militias who control much of southern Syria are behind the surge in smuggling and support the smugglers' operations. Hezbollah denies the accusations.

Jordanian officials say they have raised their concerns with Syrian authorities and Russia, a main ally of Syrian President Bashar al Assad, whose military police maintain a presence in southern Syria.

Syrian authorities have in recent months announced several major interceptions of drugs destined for Gulf markets and say they are cracking down on domestic production of Captagon.

U.N. drug experts say Syria, shattered by a decade of civil war, has become the region's main production site for drugs also destined for Jordan, Iraq and Europe.