Air forces have carried out a fresh missile bombardment on rebel-held sections of Aleppo for the first time in three weeks, activists in the besieged city have said.
The British-based Syrian Observatory for Human Rights said the airstrikes struck three neighbourhoods.
There were no immediate details on casualties.
Britain has urged Russia to stop the latest bombardment of Aleppo.
There are reports of multiple deaths in the war-torn Syrian city after the first airstrikes in nearly a month.
International Development Secretary Priti Patel denounced "sickening" reported attacks hitting hospitals and refugee camps during the renewed assault and said they could constitute violations of humanitarian law.
Foreign Secretary Boris Johnson warned that the resumption of airstrikes made a resolution to Syria's civil war even more remote.
In a statement released by the Department for International Development, Ms Patel said: "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."
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.
But Russian Defence Ministry spokesman Major General Igor Konashenkov insisted that the Russian military did not strike any targets in Aleppo.
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