Syria’s military announced Thursday that it has recaptured the historic city of Palmyra from the Islamic State group as the militants’ defenses crumbled and fighters fled in the face of artillery fire and intense Russia-backed airstrikes.

The development marks the third time that the city — famed for its priceless Roman ruins and archaeological treasures the Islamic State had sought to destroy — has changed hands in one year.

It was also the second blow for the Islamic State in Syria in a week, after Turkish-backed opposition fighters seized the Syrian town of al-Bab from the militants on Feb. 23, following a grueling three-month battle. In neighboring Iraq, the Sunni extremist group is fighting for survival in its last urban bastion in the western part of the city of Mosul.

For the Syrian government, the news was a welcome development against the backdrop of peace talks underway with the opposition in Switzerland.

“You are all invited to visit the historic city of Palmyra and witness its beauty, now that it has been liberated,” the Damascus envoy to the U.N.-mediated talks, Bashar Jaafari, told reporters in Geneva.

The Damascus military statement said troops gained full control of the desert town in central Syria following a series of military operations carried out with the help of Russian air cover and in cooperation with “allied and friendly troops” — government shorthand for members of the Lebanese militant group Hezbollah fighting alongside Syrian President Bashar al-Assad’s forces.

Islamic State defenses around Palmyra had begun to erode on Sunday, with government troops reaching the town’s outskirts on Tuesday. The state-run Syrian Arab News Agency reported earlier that government troops had entered the town’s archaeological area, a UNESCO World Heritage Site, at about midday, then the town itself, as Islamic State militants fled.

This is the Syrian government’s second campaign to retake Palmyra. It seized the town from Islamic State militants last March only to lose it again 10 months later.

Before civil war gripped Syria in 2011, Palmyra was a top tourist attraction, drawing tens of thousands of visitors each year.

Archaeologists have decried what they say is extensive damage to its ruins.

Drone footage recently released by Russia’s Defense Ministry showed new damage to the facade of Palmyra’s Roman-era theater and the adjoining Tetrapylon, a set of four monuments with four columns each at the center of the colonnaded road leading to the theater.

A 2014 report by a U.N. research agency disclosed satellite evidence of looting while the ruins were under Syrian military control. Opposition factions have also admitted to looting the antiquities for funds.

Islamic State militants have twice used the town’s Roman theater as a stage for mass killings, most recently in January, when they shot and beheaded captives they said had tried to escape their December advance. Other Islamic State killings were said to have taken place in the courtyard of the Palmyra museum and in a former Russian base in the town.

The developments in Palmyra came against the backdrop of the talks in Geneva, which have been without any tangible breakthroughs so far. Diplomats and negotiators have set their sights on modest achievements in the latest round, after a week of discussions centering on setting an agenda for future talks.

On Thursday, Staffan de Mistura, U.N. special envoy for Syria, held another round of meetings with the government delegation and opposition groups.

Russian Deputy Foreign Minister Gennady Gatilov told reporters Wednesday that “the parties have agreed to . . . discuss all issues in a parallel way, on several tracks.”