The U.N. Human Rights Council will hold a special session on the worsening situation in the embattled Syrian city of Aleppo on Friday after a formal request from Britain, a United Nations statement said.
Britain made the request on behalf of a core group of 11 Western and Arab countries, including the United States and regional powers backing Syrian rebel forces.
Britain's letter to the 47-member forum said the special session was needed "following the most recent deterioration of the human rights situation in Aleppo, and the failure of the Assad regime and its allies to fulfil their international human rights commitments", the U.N. statement said.
Russia and Syria have halted all air strikes on eastern Aleppo, two days ahead of a planned ceasefire aimed at allowing rebels and civilians to leave the city, the Russian defence minister said on Tuesday.
Britain and the United States said on Sunday they were considering imposing additional sanctions on Syrian President Bashar al-Assad and his supporters for their actions in the war. The European Union has condemned Russia's air campaign, saying it may be guilty of war crimes, and promised to impose more sanctions on Assad's government.
The United Nations said on Tuesday that Russia's plan for a ceasefire will not mean supplies get into eastern Aleppo because Russia, Syria and other groups fighting in the city have not yet given guarantees of safety for aid workers.
A U.N. commission of inquiry led by Brazilian expert Paulo Pinheiro has been documenting possible war crimes by all sides in Syria's conflict and collecting testimony from victims and witnesses for five years.
The panel said last month that it had a database of some 5,000 detailed interviews and information, some of which is being shared with European governments seeking to prosecute their nationals fighting as foreign militants in Syria.