Syrian regime forces and their allies have broken a three-year opposition siege on two towns in northwest Syria, regime and opposition sources said on Wednesday, cutting off a main opposition route to nearby Turkey.
The towns of Nubul and Zahraa, with an estimated population of 60,000, are connected to the Turkish border by areas under the control of YPG militants.
The YPG is the militant wing of the PYD, which is considered by Turkey to be the PKK terrorist group's Syrian extension. The PKK is recognised as a terrorist organisation by Turkey, the EU, and the US.
Turkish Prime Minister Ahmet Davutoglu referred to the advances as "worrisome," noting that "Aleppo is a corridor for life between Turkey and Syria. The help coming from all around the world reaches Syria through this aisle."
"Turkey still provides help to the region and will continue to do so; but the current situation is worrying," he said, speaking at a news conference in London on Thursday.
"This humanitarian logistic corridor is now under the invasion of these foreign fighters and regime forces [with] the support of Russian war planes," he said.
"What they want to do in Aleppo today is exactly what they did in Madaya before - a siege of starvation," Davutoglu added.
Al Manar, the television channel of Lebanon's Hezbollah militant group, joined Syrian regime media in reporting the breakthrough, which it said came after regime forces moved in from towns secured in a recent offensive in northern Aleppo Province.
A member of Levant Front, which is a Syrian opposition group, said the siege was broken "after three days of legendary resistance by the revolutionaries facing the Russian military machine and after more than 500 raids by Russian bombers."
"Less than 3 km separate the regime from cutting all routes to opposition-held Aleppo," said Rami Abdulrahman, head of the Syrian Observatory for Human Rights.
"It did in three days what it failed to do in 3-1/2 years," he added.
Also on Wednesday UN-mediated talks in Geneva to end the war in Syria were paused until Feb. 25. UN envoy Staffan de Mistura said they had not failed but urgently needed help from international backers led by the United States and Russia.
Syrian regime forces and their allies meanwhile conducted offensives against opposition forces in the south of Aleppo, once Syria's biggest city and commercial center, and against DAESH to the east of the city split between regime and opposition control.
Alongside heavy Russian aerial support, the advances have been made possible by Lebanese Hezbollah and Iranian-backed militia forces which support Bashar al Assad's regime.
"Russia has been trying to join regime areas with YPG-controlled territories aiming to take away all opposition regions. Therefore, we could say that political efforts [to find a resolution to Syrian conflict] is not so meaningful under these conditions," said Oytun Orhan, a researcher at a Turkish think-tank ORSAM.
"It is almost impossible that political negotiations could bear fruit as long as clashing forces in Syria keep fighting on the ground against each other in order to convert their military success into a political victory," Orhan added.
The Russian air strikes which began in late September tilted the war in Assad's favour after setbacks earlier in 2015 brought opposition groups close to the coastal heartland of the regime's stronghold in western Syria.
A senior regime official told Reuters that the Syrian regime forces and their allies have completely broken the siege on Nubul and Zahraa.
Al Manar TV said pro-regime militants from the besieged towns were able to link up with advancing regime forces after the town of Maarsteh al Khan fell to them.
Breaking the siege opens a direct route for the Syrian regime to PYD-controlled Afrin in northwestern Syria and brings them closer to areas run by other opposition groups near the Turkish border.
Defence strategists say the two heavily garrisoned towns could become a launching pad for the Syrian regime and its allies for wider territorial gains in northern Aleppo Province and to tighten the encirclement of the opposition-held part of Aleppo city.
A Syrian regime source claimed that a critical supply route for opposition forces between Turkey and Aleppo has been severely cut by ending the siege.
Furthermore, Syrian regime forces have reportedly pressed ahead in southern Syria where they made advances near Daraa city in the town of Atman after securing the town of Sheikh Maskin last month.