The information that Russia has struck Islamic State positions in Raqqa has been also reported by a senior French government source, cited by Reuters.
A US official told Reuters that Moscow has conducted a significant number of strikes in Syria using both sea-launched cruise missiles and long-range bombers.
Russia gave notice to Washington ahead of the airstrikes, in accordance with an agreement on air safety, US official said, adding that some of Russian strikes had targeted Raqqa, the stronghold of IS militants.
This is the second time Russia has hit Islamic State positions in Syria from the sea. The first attack was in October this year when Russian warships fired cruise missiles from the Caspian Sea to hit several Islamic State positions in Syria.
