But opposition activists from the city, which fell to Isis control nearly a year ago, accused Russian forces of indiscriminate bombing of civilians and destruction of homes and infrastructure.

“Russian planes, missiles and artillery have not stopped bombing the city indiscriminately as part of a scorched earth policy, without differentiating between humans and rocks,” activists with the Palmyra Local Coordination Committee said.

Government forces are fighting Isis seven miles from the city’s western gates in some of the most intense battles in the area in months, monitoring groups and activists said.

The Syrian government said it had control over two pathways into the city, tightening the noose on Isis fighters in the area.

Palmyra fell to Isis last May, after a one-week siege after which regime forces abandoned the city to its fate. The invasion of Palmyra sparked an international outcry over fears the militant group would destroy its monuments, some of the best-preserved from antiquity.

Isis proceeded to do just that, destroying the ancient Temple of Bel and the smaller Temple of Baal Shamin last year, as well as beheading Palmyra’s former antiquities director, Khaled al-Asaad. It also used the Roman amphitheatre to stage a brutal execution video featuring child soldiers shooting dead alleged regime collaborators.

A victory in Palmyra would be a significant morale boost for the Assad regime, which is engaged in stalled peace talks in Geneva with representatives of the opposition under UN, US and Russian auspices. It would also be a propaganda victory for Moscow, which launched a campaign to safeguard Assad’s rule last October.

Though ostensibly directed against Isis, the vast majority of the airstrikes were against the mainstream opposition and have killed 2.000 civilians, rights groups and observers have said.

It would also be a significant setback for Isis. The image of the militants stalking the ruins of the ancient oasis, a hub of the Silk Road, has been a propaganda coup highlighting the impotence of the international community. The city’s position in central Syria also provides a corridor linking the group’s territory in the eastern desert with the central provinces of Homs and Damascus, closer to the Assad regime’s power centre.

The extent of the Russian campaign in Palmyra raises questions about the scale of the Kremlin’s surprise announcement last week that it was withdrawing the majority of its forces from Syria.

The Syrian Observatory for Human Rights, a monitoring group, said Russia had carried out dozens of airstrikes on the city on Wednesday alone, and activists from the city put the figure at 40 airstrikes and a ballistic missile launch.

The activists accused Russia of carrying out hundreds of airstrikes over the past two weeks, including inside the city, where they said there was a limited Isis presence as most of the militants were situated on the outskirts. They also alleged Moscow had deployed cluster munitions in the campaign. The allegations could not be verified.

“We condemn the destruction that Russia and its army are doing to our city and our culture,” the activists said.