Turkey delivers aid across border as Syrian forces step up Aleppo assault

Rebel-held areas in and around Aleppo, Syria's largest before the war, are still home to 350,000 people, and aid workers have said they could soon fall to the government.

The Syrian Observatory for Human Rights, which monitors the war, said air strikes, thought to be from Russian planes, hit villages north of Aleppo on February 7 including Bashkoy, Haritan and Anadan, the latter two near the road to Turkey.

Russia's intervention has tipped the balance of the war in favor of President Bashar al-Assad, reversing gains the rebels made last year. Advances by the Syrian army and allied militias, including Iranian fighters, are threatening to cut the rebel-held zones of Aleppo off from Turkish supply lines.

"In some parts of Aleppo, the Assad regime has cut the north-south corridor ... Turkey is under threat," Turkish President Tayyip Erdogan was quoted by the Hurriyet newspaper as telling reporters on his plane back from a visit to Latin America.

Turkey has given refuge to civilians fleeing Syria throughout the conflict, but is coming under growing pressure from the United States to secure the border more tightly, and, from Europe, to stem the onward flow of migrants.

It is already sheltering more than 2.5 million Syrians, the world's largest refugee population.