Britain and the United States said on Sunday they were considering additional sanctions against Syrian President Bashar al-Assad and his supporters, and called on Russia to help end the Syrian conflict.
"It is vital that we keep that pressure up and there is a lot of measures we\’re proposing, to do with extra sanctions on the Syrian regime and their supporters, measures to bring those responsible for war crimes to the International Criminal Court," British Foreign Secretary Boris Johnson told reporters.
"These things will eventually come to bite the perpetrators of these crimes and they should think about it now," said Johnson, who also said there was no appetite in Europe for "going to war" in Syria.
He said it was "highly dubious" that Assad\’s government and its ally Russia were capable of retaking the city of Aleppo or winning the war, calling on Russia and Iran to show leadership to end the conflict.
"It is up to them to show mercy, show mercy to those people in that city and get the ceasefire going," he added.
He was speaking alongside U.S. Secretary of State John Kerry, who briefed nearly a dozen European and Middle Eastern allies on talks with Russia and a group of Middle Eastern countries that had taken place in Switzerland on Saturday with the aim of ending the fighting.
Kerry confirmed that the United States and its allies were considering additional sanctions over Syria, but did not name Russia as a target.
Western powers have accused Russia and Syria of committing atrocities by bombing hospitals, killing civilians and preventing medical evacuations, as well as targeting an aid convoy with the loss of around 20 lives.
Syria and Russia counter that they are only targeting militants in Aleppo and accuse the United States of breaking the ceasefire by bombing scores of Syrian troops fighting Islamic State insurgents, over which the United States has expressed regret.
"We are considering additional sanctions and we are also making clear that President (Barack) Obama has not taken any options off the table," Kerry said.