Beirut: Syria’s Al Qaida offshoot Al Nusra said on Friday it killed a captive Lebanese soldier in retaliation for the arrest by Lebanese authorities of women identified as wives of Islamist militants.

The soldier was one of more than two dozen members of the security forces taken captive by militants affiliated to the Al Nusra Front and Daesh when they staged an attack on the Lebanese border town of Arsal in August.

Lebanese authorities earlier this week said they had detained a wife of Daesh leader Abu Bakr Al Baghdadi and the wife of an Al Nusra front leader.

The women were apparently viewed by some Lebanese security elements as a possible bargaining chip with the militants to gain the release of the captive soldiers.

Al Nusra warned in the statement they would execute another prisoner among the captive soldiers “within a short period” if the Lebanese authorities did not release the women captives.

Spillover from the Syrian conflict has repeatedly jolted neighbouring Lebanon.

Militants affiliated to the Al Qaida-linked Al Nusra Front and Daesh are demanding the release of Islamists held by the Lebanese authorities in exchange for the captured members of the Lebanese security forces.

The soldier is the fourth killed by the militants since August in an attempt to put pressure on Lebanese authorities to accept a prisoner swap.

Last Tuesday, at least six Lebanese soldiers were killed by gunmen from Syria who attacked an army patrol near the border.

Shortly after the execution of Ali Al Bazzal was announced, protesters blocked a highway near his home village of Bazalia not far from Arsal. Armed men also appeared in the streets there, security sources said.

Many Sunni Syrian rebels and hardline Lebanese Sunni Islamists accuse Lebanon’s army of working with the Lebanese Shiite movement Hezbollah, which has sent fighters to aid Syrian President Bashar Al Assad, a member of the Shiite-derived Alawite minority.

Daesh has declared a caliphate and seized wide areas of Iraq and Syria, Lebanon’s neighbour to the east.

The Lebanese security forces have cracked down on the group’s sympathisers and the intelligence services have been extra vigilant on the borders with Syria.

Anger erupted in eastern Lebanon early Saturday after Al Qaida-linked Syrian extremist group the Al Nusra front said it had killed the Lebanese policeman.

The body of an unidentified Sunni man who had been shot dead was found on a road in the mainly Shiite Bekaa Valley region bordering Syria while gunmen abducted an unknown number of Sunni residents from the area, security sources said.

Angry residents were blocking roads and set fire to tyres in the village of Bazzalieh, an AFP correspondent at the scene said.

The flare-up came after Al Nusra posted a photograph that it said showed the execution of detained Lebanese policeman Ali Al Bazaal, in a statement on its Twitter account picked up by the SITE terrorism watchdog.

Bazaal was one of around 30 Lebanese soldiers and policemen abducted by jihadists in August during fighting in Arsal.

“If the sisters that were unjustly arrested are not released, then after a short period of time the death sentence will be executed against another prisoner we hold,” Al Nusra said.

Lebanese security sources said they were trying to verify the claim.