US Secretary of State John Kerry has defended Russia's efforts in ending hostilities in Syria, saying Russia has played a "constructive role" in the country.

"If they hadn't played a constructive role, we would not have gotten the chemical weapons out of Syria, and they would be in the hands of ISIL today. And if they hadn't played a constructive role, we would not have gotten the cessation of hostilities or everybody at the table in Geneva," he said.