BEIRUT, Lebanon — Islamic State fighters appeared close to retaking Palmyra, Syria, on Saturday, just nine months after Syrian government forces drove them from the desert city, where they had terrorized residents and blown up irreplaceable ancient monuments.
Residents said Islamic State militants were battling soldiers in the city’s center, after retaking outlying oil fields and nearly encircling the city over the past week as the government and its allies were focused on a pivotal battle in Aleppo, further north.
Losing Palmyra for a second time would be a major symbolic and military blow for the Syrian government, which boasted about its reconquest of the city in March, after 10 months of Islamic State rule.
Russia, the government’s main ally, which had helped with air support and advisers, flew in an orchestra to play a victory concert in Palmyra’s ancient amphitheater that month.
A victory for the Islamic State, however, is not necessarily a major turning point for the group. The Islamic State is losing ground and on its heels. Early this week, its strategic stronghold in Surt, Libya, fell to American-backed fighters. Taking Palmyra, a lightly fortified city, while the Syrian government’s attention was elsewhere was a tactically easy move, which has grabbed headlines and boosted the militants’ morale.
The Russians also established a small base in the city, but residents said all Russian troops had pulled out in recent days as the militants approached. Local activists also said that Russian warplanes had pounded Palmyra after the Islamic State captured much of it. Tass, a Russian state news agency, reported that “reinforcements have been relocated to repel Islamic State’s attack from the south.” The claim could not be independently verified.
The battle for Palmyra comes as the government has been scoring its most important victories in years in Aleppo, once Syria’s largest city.
The army and allied militias there have retaken most of the eastern half of the city. East Aleppo has been held for four years by rebels opposed to President Bashar al-Assad.
Another battle, also unfolding on Saturday, may further complicate the government’s war strategy. A rebel coalition backed by Turkey made advances against the Islamic State, also known as ISIS or ISIL, in the city of Al Bab in northern Aleppo Province, an area that the Syrian government hoped to conquer from the group.
Residents were in a state of fear and anxiety, according to activists from the Local Coordination Committee of Palmyra, a group that opposes both Mr. Assad’s government and the Islamic State’s self-described caliphate.
The activist group said that residents were being abandoned by government forces, which had withdrawn from several areas. The events echoed those of spring 2015, when most government forces left the area, leaving residents and a few junior soldiers at the hands of the Islamic State.
Many of those who remained were executed.
On Saturday, pro-government social media accounts reported that Russian advisers and other “allies” — possibly including militiamen from Iraq and the Lebanese group Hezbollah — had abandoned Palmyra as the Islamic State approached, leaving Syrian government troops to fend for themselves.
Hezbollah played a major role in the battle to take back Palmyra nine months ago, a victory it sought to publicize in order to show that it, too, was battling terrorism and saving the ancient ruins from further destruction.
On Thursday, 34 Syrian soldiers were reported killed in an Islamic State bombing at a location on the outskirts of Palmyra known as the Qatari castle.
The Islamic State’s advance came as state news media broadcast statements about the government’s victory in East Aleppo.
State television has painted a rosy picture, suggesting that reconstruction work in Aleppo could soon begin and some of the five million refugees outside Syria could start returning home.
Mr. Assad, however, called the Aleppo siege a major victory, but said it would not end the war.