BEIRUT — Syrian warplanes pounded a rebel-held neighborhood in the central city of Homs on Sunday, killing at least three and wounding dozens, opposition activists said, and President Bashar Assad’s forces pushed ahead in Syria’s offensive on the historic town of Palmyra held by the Islamic State.

The Britain-based Syrian Observatory for Human Rights and progovernment media said troops were about 6 miles west of Palmyra, which is home to some of the world’s most treasured archeological sites.

ISIS overran the city, prized for its ancient Roman archeological ruins, for a second time in December. In March last year, government forces had captured the town, ending a 10-month rule by the extremists.

The Observatory said government forces and their allies now control hills that oversee three gas fields west of the town amid intense airstrikes. Syrian troops and their allies launched a wide offensive toward Palmyra in mid-January under the cover of Russian airstrikes.

The government-controlled Syrian Central Military Media confirmed that troops are now a few miles away from the town, which is home to the UNESCO heritage site for which Palmyra is famous and which has already suffered massive destruction at the hands of ISIS.

The Islamic State group has been under pressure in Iraq and Syria over the past months and the march toward Palmyra comes days after the extremists lost the northern town of al-Bab to Turkish troops and Turkey backed opposition fighters. Iraqi forces are also on the offensive to capture the western part of the northern Iraqi city of Mosul.