Nearly 500,000 children live in besieged areas across Syria, the UN has warned, a figure that has doubled in less than a year.

"For millions of human beings in Syria, life has become an endless nightmare – in particular for the hundreds of thousands of children living under siege. Children are being killed and injured, too afraid to go to school or even play, surviving with little food and hardly any medicine," said Anthony Lake, UNICEF executive director.

"This is no way to live – and too many are dying."

UNICEF warned that around 100,000 children are living under siege in Aleppo alone, where thousands are attempting to flee increased violence.

Across 16 besieged areas in Syria, hundreds of thousands of children are almost completely cut off from sustained humanitarian aid and basic services.

Volunteers have been forced to build basement playgrounds, schools and hospitals to try to cope with the crisis.

UNICEF renewed its call to lift the sieges across Syria, and to facilitate immediate humanitarian access to all areas.

The call comes as a priest in Aleppo urged Christians around the world to join Syrians in praying for peace.

Father Ibrahim Alsabagh, priest of the Latin parish of Aleppo, told Asia News that civilians are "exhausted" by war and the city has become "powerless and fearful".

"We are all waiting to see what will happen in the coming days. Families, west and east, are exhausted; they only want peace in the face of an increasingly difficult life," he said.