The Islamic State extremist group has regained control of a string of Syrian villages near the Turkish border, reversing recent rebel gains in the strategic area, a monitoring group reported Wednesday.
Islamic State fighters have now recaptured areas between the town of al-Rai and the village of Dudian, which fell to rebels in March, Rami Abdel Rahman, the head of the Britain-based Syrian Observatory for Human Rights, told dpa.
The development is a blow to the Syrian opposition and its Turkish backers who had hoped that rebels could push into the Islamic State-controlled region of eastern Aleppo province.
The eastern Aleppo area is the extremist group's last outlet to the Turkish border, and Syrian rebels and Ankara had been anxious to pre-empt rival offensives from Syrian government and Kurdish forces, according to analyst Fabrice Balanche writing for the Washington Institute for Near East Policy.
The rebels had captured al-Rai itself, which they said was an important smuggling route for the extremists, on April 8, but lost it again three days later.
Ahmed al-Ahmed, a spokesman for one of the main Islamist rebel groups in the area, confirmed to dpa through a phone message that they lost Dudian, Jariz, Tel Hussien and other small areas.
"The battles in northern Aleppo are tit-for-tat: one time they take villages and other times we regain them, or vice versa," al-Ahmed, of the Faylaq al-Sham Brigade, said.
Rebels in the area have been cut off from Aleppo city and the main rebel strongholds in north-western Syria since a Russian-backed government offensive in early February.
Government forces appear to be preparing to besiege rebel-held areas of Aleppo, Syria's largest city before the war, while the Kurds seek to link up an enclave north-west of the city with their main territory further east.
A US and Russian-backed ceasefire, which excludes Islamic State and al-Qaeda fighters, officially remains in force but, on the ground, fighting and shelling have intensified in recent weeks.
The Syrian opposition last week suspended its participation in peace talks in Geneva, citing a lack of progress on humanitarian issues and escalating ceasefire breaches.