Syria’s government ­declared Sunday that its forces had seized Palmyra from the Islamic State, driving the militant group out of the archaeologically significant city and dealing it a major blow.

Retaking the desert city, a UNESCO world heritage site known for its Roman-era ruins, is a substantial victory for Syrian President Bashar al-Assad. His forces appear to have seized the upper hand in a devastating civil war that has turned into a dangerous proxy conflict.

Palmyra’s capture also is a victory for Russia’s military involvement in Syria, an intervention launched in September that has inflicted heavy damage on rebel groups and bolstered Assad, a Russian ally.

Taking the city helps clear a path for pro-government forces to possibly push on to Raqqa, the city in eastern Syria that is the Islamic State’s self-declared capital.

“The liberation of the historic city of Palmyra today is an important achievement and another indication of the success of the strategy pursued by the Syrian army and its allies in the war against terrorism,” state television quoted Assad as saying during a meeting with a French delegation, the Reuters news agency reported.

In a telephone conversation, Russian President Vladimir Putin congratulated the Syrian leader, Russian news agencies reported.

Putin this month announced that he would draw down the bulk of Russia’s forces in Syria. But many of Russia’s warplanes have remained in the country, and they provided crucial air support for the nearly month-long offensive to retake Palmyra, about 150 miles northeast of the capital, Damascus.

State television showed troops entering what it said was Palmyra. The images depict a deserted city that appears to have suffered heavy damage from fighting. Streets are covered with rubble and the facades of buildings heavily pockmarked.

Citing an unnamed military official, the state-run Syrian Arab News Agency said pro-government forces had “eliminated the last gatherings of ISIS terrorists in the city and destroyed their last hideouts.” The Islamic State is also known as ISIS.

But an activist and the Syrian Observatory for Human Rights, a Britain-based monitoring group, said that even though most Islamic State militants had withdrawn, clashes continued in the northeastern corner of the city.

“ISIS sent two car bombs to the city center a while ago,” said Khalid al-Homsi, an activist from the city who resides in Turkey.

A photo released by the Syrian official news agency SANA shows damage to the Palmyra citadel following fighting between government forces and Islamic State militants on Sunday, March 27. (Uncredited/AP)

The extent of the damage to Palmyra’s 2,000-year-old ruins remains unclear. Images posted on social media purport to show ­recent explosions in the vicinity of the city’s medieval citadel.

After taking over Palmyra in May, the Islamic State began destroying some ancient monuments, including the 1st-century Temple of Bel and the Arch of Triumph, which a Roman emperor built in about A.D. 200. The extremist group also used the monuments as forums for executions.

Islamic State militants have carried out large-scale anti-idolatry campaigns, destroying precious artifacts in the parts of Syria and Iraq under its control. Using extremist interpretations of Islam to justify the destruction, the group often targets pre-Islamic artifacts.

The recapturing of Palmyra is the latest sign that the group has been badly weakened in its strongholds in Iraq and Syria by both pro-Assad fighters and U.S.-backed Kurdish and Arab forces.

Late last year, Iraqi forces drove Islamic State militants out of the city of Ramadi. In February, Kurdish fighters defeated the group at al-Shaddadi, a town in eastern Syria.

U.S. military officials estimate that the group has lost more than 40 percent of the territory it held in Iraq and more than 20 percent in Syria.

The attack on Palmyra comes amid a nationwide cease-fire that has substantially reduced violence, despite numerous violations claimed by government and anti-government fighters.

The partial truce. which does not include the Islamic State, has received strong backing from Russia and the United States, even though the two powers support opposing sides in the conflict.

Read more:

Palmyra’s Temple of Bel withstood 2,000 years of war and invasions — until the Islamic State

Why the ancient city of Palmyra, seized by the Islamic State, matters

The Islamic State has lost more than a fifth of its territory, says report

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