The Syrian army on Wednesday cut the last supply route linking opposition forces in the northern city of Aleppo to the Turkish border, a military source said, in a major blow to the rebels.
The source said the army had broken a three-year rebel siege of two government-held Shiite villages, Nubol and Zahraa, and taken control of parts of the supply route.
"Heavy air strikes by Russian planes" supported the army in its advance, the Syrian Observatory for Human Rights monitoring group said.
The development came as U.N. special envoy for Syria Staffan de Mistura in Geneva presses ahead with efforts to engage Syria's warring sides in indirect peace talks aimed at ending almost five years of conflict.
Russian planes have carried out heavy air strikes throughout the area north of Aleppo city in the last few days.
The government advance comes almost exactly a year after the failure of a similar regime offensive aimed at reaching Nubol and Zahraa and severing rebel supply lines into Aleppo city.