A U.N. spokeswoman says that intensified fighting between Syrian government forces and rebels in contested Aleppo has completely cut off the only road allowing access for humanitarian aid deliveries into the rebel-held part of the city.

Alessandra Vellucci said on Tuesday that the Castello road, considered the only access in and out of eastern Aleppo, has been rendered "impassable" since hostilities there worsened last week.

Vellucci says the U.N. estimates that 300,000 people depend on the road, which allows for the flow of supplies, goods and civilians into the area.

She says the U.N. continues to receive "distressing reports of aerial bombardment and shelling on civilian locations in both western and eastern Aleppo."

She called on all sides to protect civilians and ease access for humanitarian access to all.