Isis has withdrawn its troops from Palmyra in the face of heavy Russian air strikes, a monitoring group said, one day after it reentered the ancient city.
The Russian Defence Ministry said in a statement on Sunday that it had assisted the Syrian army in repelling all Isis attacks on Palmyra overnight.
Russian jets carried out 64 air strikes during the operation to defend the ancient city, killing more than 300 militants, the ministry said.
The new battle for Palmyra comes almost nine months after Isis was driven out of the city at the end of March.
That was not before they had inflicted widespread damage to the city's ancient Roman structures, including the destruction of the 2,000-year-old Temple of Bel.
Militants first overran Palmyra in May 2015, after which they forced residents of the neighbouring modern city to live by their brutal interpretation of Sharia law.
The occupation also saw the murder of the city’s 81-year-old director of antiquities, Khaled al-Asaad, and Palmyra's ruins used as the backdrop for a series of gory executions and propaganda videos.
Isis fighters are now understood to have fallen back to orchards on the outskirts of Palmyra and the modern city of Tadmur.
They have been advancing on Palmyra since Thursday, when the group launched a surprise attack on the Syrian army and pro-government Shia militias.
Monitors with the anti-Isis Palmyra Coordination Committee (PCC) said militants approached from “more than one axis” on Saturday, fighting their way into the al-Amiriyah district before targeting the city’s citadel.
The same group reported that Isis had downed a Syrian government fighter jet in nearby Jazal.
Isis has been mounting a concerted propaganda effort to highlight the campaign as its forces are beaten back in its Iraqi stronghold of Mosul.
Amaq, the self-styled news agency controlled by Isis, released footage of battles appearing to show its fighters advancing against the Syrian army through the desert on Saturday, while videos sent out the previous day showed a huge suicide car bombing hit an army checkpoint on a road approaching the city.
