In Syria, Russian-backed government troops have entered the ancient city of Palmyra after days of intense clashes with Islamic State militants.

The Syrian Observatory for Human Rights, which monitors the conflict, says regime troops have pushed into the southwest corner of the city. Observatory Director Rami Abdel Rahman says advances inside the city are slow, as ISIS planted mines in areas where it retreated.

State news agency SANA reports that the army took control of Mount Altar, a strategic point west of the city's famed ruins.

Hours before the incursion, local activists said ISIS warned civilians via loudspeaker to flee. Most residents left Palmyra when ISIS took over the city in May 2015, but those who remained have now largely fled to the cities of Raqqa or Deir Ezzor amid merciless airstrikes. Activist Khaled al-Homsi says people are fleeing deeper into ISIS-held territory because the path to safer, government-held zones has been blocked by the fighting.

Palmyra is a strategically important location along a desert highway in central Syria. Retaking the city would mean cutting off a key route to the sprawling ISIS heartland, which spans across the Iraqi border to the east.

Russian Foreign Minister Sergei Lavrov said earlier this month that U.S. counterparts had suggested a "division of labor" against ISIS in Syria. Russia's air force would focus on retaking Palmyra, while the U.S.-led coalition would focus on Raqqa farther north.

A victory in Palmyra would also hold symbolic value for Syria's regime. Since ISIS overran the city last May, the group has blown up temples and statues dating back millennia and killed suspected regime supporters. The extremist group has also used the city's ruins as a showcase for its brutal killings. One of the Islamic State's first acts was to stage a mass execution in the ancient Roman theater, employing child fighters to shoot some two dozen men accused of fighting for the regime in the back of the head.

The killings extended to civilians, as well. In August 2015, ISIS beheaded 81-year-old Khaled al-Assad, a renowned archaeologist who was beloved for his knowledge of the ancient city. A week after his murder, the militants rigged the Baal Shamin temple with explosives and then detonated the first-century structure.

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