The Islamic State (IS) group has retaken the Syrian city of Palmyra, hours after Russian air strikes appeared to have driven it back.
The governor of Homs province, Talal Barazi, said government forces were now regrouping outside the ancient city, preparing to launch a fresh assault.
IS held the city from May 2015 until it was forced out in March this year.
Correspondents say IS appears to have taken advantage of the government’s focus on Aleppo, further north.
Mr Barazi confirmed the withdrawal from Palmyra but insisted “the army is using all means to prevent the terrorists from staying”.
Activists in the city said militants were going door to door looking for any remaining forces loyal to President Bashar al-Assad.
IS re-entered the city and its nearby ancient ruins – a Unesco World Heritage site – on Saturday, after launching an offensive earlier in the week.
The UK-based Syrian Observatory for Human Rights said on Sunday morning that “intense” bombing from Russian planes had forced IS to withdraw to the orchards on the city’s outskirts.
The Russian defence ministry said it had carried out 64 strikes during the operation, and claimed to have killed more than 300 militants.
The Syrian army has also sent reinforcements to the city, reportedly diverting troops from Aleppo.
The observatory later reported that militants had again fought their way into the town, forcing government forces to retreat to the south.
Reports said IS militants had attacked with suicide car bombs and artillery.
Palmyra is seen as strategic for IS because it lies close to oilfields.
IS destroyed a number of monuments and beheaded the archaeological director during its 10-month occupation of the site and the adjacent city of Tadmur.
Two 2,000-year-old temples, an arch and funerary towers were left in ruins.
Maamoun Abdulkarim, a Syrian official for antiquities, said the contents of Palmyra’s museum had been transferred to Damascus but he feared for the safety of the ancient ruins.
“I fear they will be more vengeful,” he told the Associated Press.
The jihadist group, which has also demolished several pre-Islamic sites in neighbouring Iraq, believes that such structures are idolatrous.
The latest battle in Palmyra happened as the Syrian army closed in on the remaining rebel-held area of the city of Aleppo.
Thousands of civilians are streaming out of rebel-held areas of eastern Aleppo
Rebel forces said on Saturday that they had halted the advance of government forces in the pockets they still control in Aleppo.
One rebel commander said a reason for the slowed government advance could be the redeployment of troops to Palmyra.
However, the Syrian government has been continuously advancing on the rebel areas, backed by Russian air support, and now reportedly controls 93% of the city.
A rebel official told Reuters news agency that his forces faced “death or surrender” as their area of control continued to shrink.
On Saturday, US Secretary of State John Kerry called on the Syrian government and the Russian military to “show a little grace” as they mopped up the remaining rebel-held areas of Aleppo.
US and Russian officials are continuing talks in Geneva over the possible evacuation of civilians and rebel fighters from Aleppo, but analysts say an agreement looks unlikely.
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