Britain has called on Russia to halt the latest bombardment of Aleppo, amid reports of multiple deaths in the first airstrikes on the war-torn Syrian city in nearly a month.
International Development Secretary Priti Patel denounced "sickening" reported attacks striking hospitals and refugee camps during the renewed assault and said they could constitute violations of humanitarian law.
And Foreign Secretary Boris Johnson warned that the resumption of airstrikes made a resolution to Syria's civil war even more remote.
Meanwhile, actress Carey Mulligan added her voice to calls from charity War Child for Prime Minister Theresa May to take action against those responsible for the suffering of a quarter of a million civilians believed to be trapped in eastern Aleppo.
According to reports, Russia used jets from the aircraft carrier which passed through the English Channel last month, as well as long-range missiles, to target rebel-held parts of Aleppo early on Tuesday.
The attack began just hours after a phone conversation between President Vladimir Putin and and US President-elect Donald Trump in which the Kremlin said each spoke of the need to "work together in the struggle against the number one common enemy – international terrorism and extremism" in the context of Syria.
The administration of US President Barack Obama has been trying for months to negotiate a ceasefire in Aleppo, which has become the focus of the long-running struggle between Syrian President Bashar Assad and the rebels seeking to oust him.
In a statement released by the Department for International Development, Ms Patel said: "Russia must call a halt to the new wave of bombs hitting the besieged city of Aleppo.
"More than a quarter of a million people are trapped and running out of food in the city. This will only worsen an already desperate humanitarian situation.
"I urge Russia and the Assad regime to prove that they can show restraint."
Ms Patel added: "Reports of air strikes hitting hospitals and camps full of displaced Syrians are not only sickening but could also violate International Humanitarian Law.
"It is essential that supplies of food and medicine can get through to those who need them, and that aid workers get the access they need to save lives."
Mr Johnson said: "The resumption of airstrikes on the besieged people of east Aleppo increases the terrible suffering of the innocent civilian population and moves us further away from a resolution to this tragic conflict.
"As I have said many times, Russia has a unique opportunity to persuade the Syrian regime to end its destructive military approach, allow full humanitarian access to all besieged areas in Syria, and commit to a political settlement which ends the bloodshed."
War Child called on the UK Government to lead the international community in implementing a robust strategy to end the attacks.
The charity, which supports children affected by conflict, said Mrs May should consider targeted sanctions against those responsible for war crimes, as well as the introduction of 'no-fly' and `no bombing' zones to end attacks on civilian areas.
Miss Mulligan, a War Child global ambassador, said: "How many more children need to die before the world does something to stop these crimes?
"I know that the Prime Minister shares my revulsion at this assault against Aleppo's children – I therefore call on her to work with our international allies to act now and bring these appalling crimes to an end. We cannot stand by and let this happen again."
The UK-based Syrian Observatory for Human Rights and other groups said air strikes hit at least eight neighbourhoods in Aleppo city, killing at least 10 people.
But Russian Defence Ministry spokesman Major General Igor Konashenkov insisted that the Russian military did not strike any targets in the city of Aleppo, adding that Russian and Syrian warplanes have not conducted any raids on the city for four weeks.