Two rebel groups are leading the push. One is Hayat Tahrir al-Sham ( HTS ), which emerged from al-Qaeda’s Syrian affiliate. It cut ties with the jihadist group in 2017 and has since set up a provisional government in rebel-held Idlib province in north-west Syria. The other faction, the Syrian National Army ( SNA ), is a Turkish proxy.

President Putin’s fledgling Mediterranean flotilla may have to retreat to ports in Libya and Algeria or to the Baltic.

Russia said on Wednesday that it strongly backs the actions of the Syrian leadership to counter an offensive by what it said were terrorist groups receiving support, including drones and training, from outside the country.

Russia and Iran have offered military and diplomatic support to the Syrian government as it tries to stanch a major rebel advance.