The UK will provide a further £20 million of aid for Syria, Theresa May has said, as she condemned Bashar Assad and his Russian and Iranian supporters.
The Prime Minister said the Assad regime must allow the United Nations to ensure the safe evacuation of civilians from Aleppo following the bloody battle for the Syrian city.
She was speaking after European Union leaders in Brussels called for an immediate ceasefire in the civil war which has torn the country apart.
The European leaders heard from eastern Aleppo’s mayor Brita Hagi Hasan, who pleaded for help.
Mrs May said: "We have discussed a number of issues here today at this European Council meeting, including how to deal with migration issues, also strengthening Europe's security.
"But perhaps the most important issue we discussed was the appalling situation in Syria.
"We heard from the mayor of eastern Aleppo, he had one plea for us: to allow the safe evacuation of the people in the city.
"President Assad and his backers, Russia and Iran, bear responsibility for the tragedy in Aleppo.
"They must now allow the United Nations to ensure the safe evacuation of the civilians who are left there.
"The UK is going to provide a further £20 million of practical support for those who are most vulnerable.
"The mayor of east Aleppo said to us that we can't bring back those who are lost but we can save those who remain and that is what we must now do."
The EU leaders accused the Assad regime, backed by Moscow and Tehran, of "the deliberate targeting of civilians and hospitals”.
They said "hostilities in Syria must cease immediately” and pledged to work with partners under the auspices of the UN towards a peaceful transition.
International Development Secretary Priti Patel said the UK was urgently sending blankets, medical kits, clean water and food for civilians from Aleppo.
She said the aid would "mean the difference between life and death for those fleeing Aleppo and those caught in freezing conditions in the city after being systematically bombed from their homes by the Syrian regime and its Russian allies".
Ms Patel added: "Protecting innocent civilians must be an absolute priority. It is paramount that aid agencies now get the unfettered, secure access they need to save lives inside east Aleppo."