The Russian military has fired multiple cruise missiles from its ships in the Mediterranean aimed at the Isis stronghold of Raqqa, according to reports.
Vladimir Putin has pledged to escalate his military campaign in Syria after it was confirmed that a bomb brought down a Russian airliner over Sinai.
US officials were quoted by the Reuters news agency as saying Russia had launched a “significant number” of strikes in Syria using both sea-launched cruise missiles and long-range bombers.
The French daily Le Monde cited senior French government officials as saying Russian missiles had struck Isis positions in Raqqa, its de facto capital in its Syrian territories.
According to reports, Russian officials gave their US counterparts notice ahead of the strikes, in a sign of closer cooperation between the two states after talks between Vladimir Putin and Barack Obama at the G20 summit.
Videos showing alleged cruise missiles flying and crashed in Syria appeared across social media on Tuesday, though their provenance could not be immediately verified.