Pope Francis has made a last-ditch appeal to President Bashar al-Assad of Syria appealing for an end to the terrible violence and destruction in which so many innocent people are dying.

Unusually, the private correspondence was released by the Vatican, an indication of the growing level of international concern at the atrocities taking place in Aleppo where trapped civilians are begging loved ones to kill them for fear of what will happen to them if captured.

The Vatican also decided to release details of the correspondence after it was published on a website in the region.

He wrote as Unicef warned that thousands of children have been separated from their parents and are trapped in a building which is currently under fire. Unicef also warned that extra-judicial killings of children are taking place.

Pope Francis wrote to Assad through Cardinal Mario Zenari, Apostolic Nuncio to Syria, appealing for "an end to the violence and the peaceful resolution of hostilities" as the cycle of bombings reduced Aleppo to little more than a field of death and destruction.

In a communiqué, the Holy See Press Office said: "In naming Archbishop Mario Zenari to the College of Cardinals, the Holy Father sought to show a particular sign of affection for the beloved Syrian people, so sorely tried in recent years.

"In a letter sent through the new Cardinal, Pope Francis expressed again his appeal to President Bashar al-Assad and to the international community for an end to the violence, and the peaceful resolution of hostilities, condemning all forms of extremism and terrorism from whatever quarter they may come, and appealing to the President to ensure that international humanitarian law is fully respected with regard to the protection of the civilians and access to humanitarian aid."

Assad forces are inching closer to taking the last few quarters of Aleppo that are still occupied by rebels. As many as 80,000 civilians are trapped there. 

Among those tweeting with increasing desperation is seven-year-old Bana:

Aid workers are also trapped amid the rubble and destruction but a cease fire is needed before people can be rescued. The House of Commons today debated whether intervention should be considered as Aleppo moved further into humanitarian crisis with little indication that Assad is heeding appeals from the Pope or anyone else.