The United States on Wednesday denounced Russian air strikes in and around the Syrian city of Aleppo, saying they were targeting opposition groups and civilians and were harming faltering attempts at peace, AFP reports.

"It is difficult in the extreme to see how strikes against civilian targets contribute in any way to the peace process now being explored," State Department spokesman John Kirby said, after the UN suspended peace negotiations until February 25.

Moscow has consistently said that it is going after "terrorist organizations" in Syria, including the "Islamic State" (ISIS) terrorist group. But the Syrian opposition - and Western countries - say the Russian strikes have almost entirely targeted other rebel groups, many of them backed by the West, Gulf states and Turkey.