Syrian regime forces backed up by allied Shiite militias and Russian airstrikes moved to encircle rebel held eastern Aleppo on Thursday after cutting a key supply line to Turkey that could change momentum in the five-year civil war.

Heavy aerial bombardment and a ground offensive north of Aleppo city since Monday gave regime forces the impetus to retake Nubul and al-Zahraa, two towns loyal to the regime that had been under rebel siege for three years.

Syrian state television on Thursday showed Hezbollah and Syrian regime forces enter the two villages to crowds of cheering loyalists. A similar offensive early last year before Russia's intervention stalled, an indication that months of airstrikes are changing the tide on the battlefield.

The regime advance brings Syrian President Bashar al-Assad's regime closer to achieving a major battlefield objective. After cutting off the supply route from Azaz, near the Turkish border, to Aleppo, rebel fighters in what was before the war Syria's largest city are only connected to parts of rebel held Idlib by a narrow strip of land northwest of the city.

The offensive came as UN-mediated peace talks in Geneva between the regime and opposition kicked off, then stalled as the opposition demanded an end to sieges of pro-opposition cities, the release of prisoners and halt to bombardments.

Germany, the United States, France, the UK and UN all condemned the Russian-backed offensive on Thursday as the reason why peace talks collapsed, and they urged all sides to return to the negotiating table.

"The coming days should be used to get back to the table, not to secure more gains on the battlefield," UN Secretary-General Ban Ki-moon said at a donor's conference in London.

In response to hundreds of airstrikes and the continuing offensive, tens of thousands of civilians have started to move towards the Turkish border.

cw/sms (AFP, AP, Reuters)