Islamic State fighters on Monday took back a key village on the Syrian-Turkish border, a monitoring group said, just days after rebels had seized control in the hope of cutting off the extremists' access to Turkey.
According to the Britain-based Syrian Observatory for Human Rights, Islamic State regained control over al Rai village, in the northern Aleppo countryside, which rebels say is an important smuggling route for extremists.
The head of the Observatory, Rami Abdel Rahman, told dpa that the rebels also lost six additional villages, reversing much of last week's gains.
"This is considered a great loss for the rebels, and it proves that without airforce backing no one can hold grounds," Abdel Rahman said.
The opposition fighters managed to take control of al Rai with the help of US-led airstrikes, rebels have told dpa.
The rebels are also looking to seize Dabiq from Islamic State, as the town holds symbolic importance for the jihadists and losing it would be a blow to morale.
Meanwhile, Syrian government forces and their allies were massing troops on the southern Aleppo front in what appeared to be preparations for a battle in the area.
Syrian government troops have been controlling the western part of Aleppo, while a patchwork of rebel forces holds the eastern sector.
Activists in the area say that aerial activities and raids have increased in the last day.
Also on Monday, UN Special Envoy to Syria Staffan de Mistura met with Syrian officials and discussed the peace talks due to be held in Geneva on April 13.
"The Geneva talks' next phase is crucially important because we will be focusing in particular on political transition, on governance, and constitutional principles," de Mistura said after a meeting with Syrian Foreign Minister Walid al-Moallem.
He said he hoped that the upcoming talks would be "constructive."
The Geneva talks are aimed at ending the Syrian crisis which so far left more than 260,000 dead since the uprising erupted in 2011.
The Syrian opposition has insisted repeatedly that there will be no role for President Bashar al-Assad in the future of Syria at a time when the regime says the people of Syria should decide on their fate.
State news agency SANA said, al-Moallem reiterated Syria's position regarding the political solution of the crisis and the commitment to "an intra-Syrian dialogue led by Syria without preconditions."
De Mistura also discussed the fragile ceasefire which had come into effect in Syria on February 27.
"We did raise and discuss the importance of protecting and maintaining and supporting the cessation of hostilities ... and we need to make sure that it continues to be sustained even when there are incidents to be contained," he said.
De Mistura and al-Maollem further tackled the issue of humanitarian access to all areas in Syria.
The UN World Food Program on Sunday had successfully managed to airdrop food and medical supplies on Deir al-Zour city in eastern Syria, where, according to the UN Office for the Coordination of Humanitarian Affairs (OCHA), around 200,000 people are living under a siege imposed by the Islamic State.