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The UN estimates that there are some 300,000 people trapped with dwindling food and medical supplies in rebel-held areas of Aleppo in Syria, which have been laid siege to by forces loyal to the Assad government.

With no way in or out, Russia said last week that it had opened four "humanitarian corridors" to allow people to leave, but their safety has been called into doubt by many living in the city, who do not trust that they will be kept safe even if they do leave.

David Nott is one of the UK's leading British surgeons and has himself worked in Syria.

He says he fears the worst for the last remaining doctors in Aleppo after he lost contact with its medics following the bombing of a number of hospitals over the weekend.