Isis have regained control of the city of Palmyra in Syria, nine months after it was driven out by Russian-backed government forces, opposition activists said on Sunday.
Russia earlier said it had repelled militants, forcing them to retreat to the outskirts of the ancient city by launching more than 60 airstrikes.
But the Britain-based Syrian Observatory for Human Rights and the Palmyra Co-ordination group say Isis militants fought their way into Palmyra on Sunday, forcing government forces to retreat to the south.
The Russia's defence ministry said the strikes had killed more than 300 Isis militants and destroyed 11 tanks and vehicles. The Syrian army also reportedly sent reinforcements to the city, reportedly diverting troops from Aleppo.
Isis held Palmyra, a Unesco world heritage site containing monumental ruins of a great city, from May 2015 until they were forced out in March this year. But they started a surprise advance on Thursday and entered the city on Saturday.
Russian war planes carried out over 60 strikes overnight halting the offensive, Russia’s defence ministry said on Sunday.
“Russian air force planes carried out 64 air strikes against the positions, convoys and advancing reserves of militants,” a defence ministry statement said. “Over the past night, Syrian government troops with active support of the Russian air force thwarted all terrorist attacks on Palmyra. The attacking militants actively used car bombs with suicide bombers, armoured vehicles and rocket artillery.”
On Saturday, the British-based Syrian Observatory for Human rights monitor said Isis jihadis had taken most of the city back and surrounded the airport. During its previous occupation, Isis beheaded the archaeological director and destroyed a number of monuments including two 2,000-year-old temples, an arch and funerary towers. The city as considered strategically important by the group because of its proximity to oil fields.
The Isis attack on Palmyra came as the Russian-backed government forces of Bashar al-Assad closed in on the remaining rebel-held area of the city of Aleppo.
On Saturday medical charities reported that chlorine gas attacks had been reported in the Kallaseh neighbourhood of Aleppo, with 25 victims reported to have experienced suffocation and difficulty breathing.
In a statement, UOSSM International, which provides medical aid to the people of Syria, said: “Targeting civilians and medical facilities with chemical weapons is a war crime. [...]We ask the OPCW [Organisation for the Prohibition Of Chemical Weapons] to fulfil its mandate and launch an immediate investigation into this attack and hold perpetrators responsible for these grievous violations to international law.”
Rebel forces said on Saturday they had halted the advance of government forces in the small pockets they still control in Aleppo, possibly due to the redeployment of troops to Palmyra, one commander told the BBC. But, backed by Russian air support, Assad’s forces now reportedly control 93 per cent of Aleppo.
On Saturday US secretary of state John Kerry joined world diplomats in Paris to call for civilians to be evacuated from the besieged city and for respect to be shown to Syria's diminished rebel forces. The bombardment of the city continued on Saturday and leaders condemning Assad's "indiscriminate" bombing as a crime against humanity.
Kerry urged Russia to show “a little grace”. The UN has expressed concern about reports that hundreds of men have gone missing after reaching government-held territory.