The city’s recapture now allows Syrian troops to move on to ISIS strongholds to the east. Video provided by Newsy

Syrian government forces backed by unrelenting Russian airstrikes recaptured the ancient city of Palmyra from Islamic State militants on Sunday, the Syrian army announced.

The announcement followed a three-week siege that left hundreds of militants dead and sent many more fleeing into the desert, the army said. It follows a string of military setbacks for the Islamic State in its efforts to create a Sunni-based caliphate from a wide swath of Syria and Iraq.

“Palmyra city is now fully cleared of ISIS terrorists after the army established complete control over all its parts, including the archaeological site and the airport,” the Syrian army said in a statement through the government controlled Syrian Arab News Agency.

The British-based Syrian Observatory for Human Rights confirmed Syrian army gains, saying government forces and Shia militias were also taking control of neighborhoods on the outskirts of the United Nations heritage site known in the region as “the bride of the Syrian desert.”

The bitter struggle against Islamic State fighters continues in Syria while a sometimes-shaky ceasefire between U.S.-backed rebels and army forces loyal to embattled Syrian President Bashar Assad continued to hold.

The Pentagon did not immediately respond to a request from USA TODAY for confirmation or comment on the Palmyra reports. The military gain provided a big win for Assad and for Moscow, both pressing their case as leaders in the war on terror.

Assad issued a statement saying the victory showed his army’s efforts were more effective than that of the U.S.-led coalition combating Islamic State in the region.

Rebel leaders dismissed Assad’s assertions. “The government wants through this operation to win the favor of Western nations by fighting against terrorism, while obscuring its responsibility as providing the reasons for the spread of terror,” Khaled Nasser, a member of the opposition coalition, told the Associated Press.

Hours before Assad’s claim of victory, Russia said it had flown 40 sorties in the area in the last day.

“The Russian warplanes delivered strikes against 158 terrorist objectives, killing over 100 militants, destroying four tanks, three artillery pieces, four depots with ammunition and five motor vehicles,” the Russian news agency TASS reported.

ISIL began evacuating civilians this week to other parts of its territories in Syria. No civilians remain in the town, a Palmyra resident who left earlier this week told the Associated Press, speaking on condition of anonymity out of safety concerns.

The battle for Palmyra had not been easy. Government forces lost at least 18 soldiers on Friday alone, including a major general, the Observatory and ISIL-affiliated media sites reported.

The Islamic State took control of the city last spring and promptly destroyed monuments dating back thousands of years, including the prized Arch of Triumph.

Mamoun Abdelkarim, head of Syria’s Archeology and Museums General Directorate, said efforts would soon begin to repair some of the damages, sending a message to terrorists. Palmyra once attracted tens of thousands of tourists every year before being battered and left unsafe by years of civil war and Islamic State efforts in the region.