Russian-backed Syrian troops pushed into a western neighborhood of the city late on Wednesday after fierce clashes with the militants.

ISIS militants withdrew from much of the Syrian oasis city of Palmyra overnight, a monitor said Thursday, but government forces paused before entering its ravaged ancient ruins because of mines.

Russian-backed Syrian troops pushed into a western neighborhood of the city late on Wednesday after fierce clashes with the militants.

By Thursday morning, ISIS had withdrawn to residential neighborhoods in the east of the city, the Syrian Observatory for Human Rights said.

“ISIS withdrew from most of Palmyra after laying mines across the city. There are still suicide bombers left in the eastern neighborhoods,” Observatory head Rami Abdel Rahman told AFP.

“Government forces have not yet been able to enter the heart of the city or the eastern parts.”

Palmyra’s ancient ruins have long been listed by UNESCO as a world heritage site.

Before ISIS entered the city in May 2015, they boasted temples, colonnaded alleys and elaborately decorated tombs that were among the best-preserved classical monuments in the Middle East.

However, the militants launched a campaign of destruction against them, the scale of which was fully revealed when government forces briefly retook the city with Russian support last year.

Satellite imagery has shown that ISIS has demolished more monuments since it recaptured Palmyra from government forces in December.

“There are no ISIS fighters left in most of the Old City, but it is heavily mined,” the Observatory chief said. Supported by Russian air strikes and ground troops, government forces have been battling through the desert for weeks to reach Palmyra.

On Wednesday, a senior military source in Damascus told AFP the army had reached a strategic crossroads leading into the city.

Syrian antiquities director Maamoun Abdul Karim told AFP he was looking forward to “the end of the nightmare” of ISIS’s rule over Palmyra.

“I feel a mix of joy and fear. Joy, because we’re sure that there will be no more damage to the archaeological site at Palmyra, and apprehension to see what has happened to the city,” Abdul Karim told AFP by telephone from Damascus.

He said he was impatiently waiting to head to Palmyra himself to see the extent of the damage.

“It’s a nightmare… When we talk about Palmyra now, we no longer talk about its beauty. It has become synonymous with fear,” Abdul Karim said.