Image copyright AFP/Getty Images Image caption People can be seen trying to escape from the violence in the city

Foreign Secretary Boris Johnson has summoned Russia's and Iran's UK ambassadors to discuss his "concern" over the countries' actions in Syria.

He said they had "failed" to uphold "humanitarian law" by not helping aid get to Aleppo when it was under siege.

Nearly 1,000 people have been evacuated from the city.

Theresa May said President Assad, Russia and Iran "bear responsibility for the tragedy in Aleppo", adding that the UK would provide £20m in aid.

Syrian government forces took nearly all remaining rebel-held parts of Aleppo this week after a four-year battle.

Mr Johnson, who met Russian ambassador Alexander Yakovenko and Iran's Hamid Baedinejad separately on Thursday afternoon, said he had conveyed the UK government's "profound concern over the situation in Aleppo".

He added: "Both Russia and Iran have failed to uphold their obligations under international humanitarian law, specifically by failing to facilitate the delivery of humanitarian aid to civilians during the months when eastern Aleppo was besieged.

"They deserve no credit for the fact that an evacuation appears to be under way today. Having inflicted such suffering on the people of eastern Aleppo, Iran and Russia cannot expect praise for allowing some people to escape at the final hour.

"Both countries need to ensure the UN now oversees the evacuation process and that all civilians and non-combatants are properly protected."

At a summit in London, Defence Secretary Sir Michael Fallon also condemned the brutality of pro-regime forces in Aleppo, and reiterated the UK's view that it sees no future for President Assad in Syria.

'Appalling situation'

Prime Minister Mrs May said the "appalling situation in Syria" was the most important item discussed by EU leaders at a European Council summit in Brussels.

She urged President Assad and his backers in Russia and Iran to "allow the United Nations to ensure the safe evacuation of the civilians who are left there".

"The UK is going to provide a further £20m of practical support for those who are most vulnerable.

"The mayor of eastern Aleppo said to us: 'We can't bring back those we have lost, but we can save those who remain.' And that is what we must now do."

A statement from the Russian Centre for the Reconciliation of Opposing Sides in Syria, part of Russia's ministry of defence, said the Syrian authorities had guaranteed the safety of all members of the armed groups who decided to leave Aleppo.