Aid trucks and ambulances entered Syria from Turkey on Sunday to deliver food and supplies to tens of thousands of people fleeing an escalating Russian-backed Assad regime assault on Aleppo, as air strikes targeted villages on the road north to the Turkish border.Russian and Syrian forces intensified their campaign on rebel-held areas around Aleppo that are still home to around 350,000 people and aid workers have said the city - Syria's largest before the war - could soon fall.The Syrian Observatory for Human Rights, which monitors the war, said air strikes, thought to be from Russian planes, hit around the villages of Bashkoy, Haritan and Kfr Hamra north of Aleppo on Sunday, the latter two lying near the road to Turkey.Russia's intervention has tipped the balance of the war in favour of Assad, reversing gains the rebels made last year. Advances by the Syrian army and allied militias, including Iranian fighters, are threatening to cut off rebel-held zones of Aleppo."In some parts of Aleppo the Assad regime has cut the north- south corridor ... Turkey is under threat," Turkish President Tayyip Erdoğan told reporters on his plane back from a visit to Latin America.Turkey's armed forces had the full authority to counter any threats to its national security, he said, although senior government officials have said the NATO member does not intend to mount any unilateral incursion into Syria.Some 35,000 civilians have arrived at Bab al-Salameh and the nearby Syrian town of A'zaz, according to the UN Office for the Coordination of Humanitarian Affairs.Many are sleeping in the open in overnight temperatures reaching minus 4 degrees Celsius.