Russian Foreign Minister Sergei Lavrov has defended his country's air strikes in Syria, saying they were targeting the same "terrorist" groups as the US-led coalition.
He rejected suggestions that Russian action was to bolster Syrian President Bashar al-Assad.
Russian jets carried out a second day of air strikes in Syria on Thursday.
But a US official said Russia had been isolated by its "indiscriminate" strikes against the Syrian opposition.
White House spokesman Josh Earnest said that if Russia was genuinely focused on fighting Islamic State (IS) it would contribute to the US-led coalition.