The Isis jihadist group has lost control of its main supply route between Syria and Turkey, the latest in a series of strategic defeats.

Syrian rebels had been closing in on the key border town of al-Rai for a number of days, and on Thursday afternoon monitoring groups said the city finally fell.

The area has been identified by the US as a priority in the fight against Isis. The rebels involved in the offensive include factions fighting under the banner of the Free Syrian Army that have been supplied with weapons via Turkey.

Speaking to the AFP News Agency, the Syrian Observatory for Human Rights said rebel factions had taken control of the northeast section of al-Rai, adding: "This is the main and one of the last crossing points with Turkey."

Meanwhile, Syrian state TV reported on Thursday that Isis militants had abducted 300 cement workers and contractors northeast of Damascus.

Palmyra recaptured by Syrian government forces Show all 10 1 /10 Palmyra recaptured by Syrian government forces Palmyra recaptured by Syrian government forces Palmyra recaptured by Syrian pro-government forces Graffiti on the ancient stones reads in Arabic ‘Shooting without the permission of the chief is prohibited’ Getty Palmyra recaptured by Syrian government forces Palmyra recaptured by Syrian pro-government forces Damaged artefacts lay inside the museum of the historic city of Palmyra Reuters Palmyra recaptured by Syrian government forces Palmyra recaptured by Syrian pro-government forces Syrian pro-government forces rest by Palmyra Citadel as they take control of the city from the hands of Isis Getty Palmyra recaptured by Syrian government forces Palmyra recaptured by Syrian pro-government forces The UNESCO world heritage site appears surprisingly intact after its recapture from the militant group Getty Palmyra recaptured by Syrian government forces Palmyra recaptured by Syrian pro-government forces Many had feared the ancient city would be destroyed following its capture by Isis in May Getty Palmyra recaptured by Syrian government forces Palmyra recaptured by Syrian pro-government forces Smoke billows from the Palmyra Citadel as Assad’s forces drive the Jihadist group from the city Getty Palmyra recaptured by Syrian government forces Palmyra recaptured by Syrian pro-government forces Palmyra is one of the ‘most important cultural centers of the world’ Unesco says Getty Palmyra recaptured by Syrian government forces Palmyra recaptured by Syrian pro-government forces Pro-government forces play football in the streets following the recapture of the city Getty Palmyra recaptured by Syrian government forces Palmyra recaptured by Syrian pro-government forces The extent of the destruction caused by Isis’ 10 month occupation of the city has yet to be fully realised Getty Palmyra recaptured by Syrian government forces Palmyra recaptured by Syrian pro-government forces The City Council of Palmyra building in ruins Reuters

The employees of the al-Badia Cement Company were kidnapped in the area of Dumeir, where militants launched a surprise attack against regime forces just a few days ago.

State-run news agency SANA quoted a source in the company as saying that there has been no success in efforts to establish contact with any of the workers.