BEIRUT (AP) — Russia said Sunday its air force has helped Syrian troops repulse an Islamic State attack on Palmyra, but opposition activists say the extremists have seized areas on the outskirts of the town, including a historic castle that overlooks ancient ruins.

The Russian Defense Ministry said it carried out 64 airstrikes overnight that killed 300 IS militants and destroyed vehicles and artillery. The head of the Britain-based Syrian Observatory for Human Rights said the militants were driven out before dawn, but regrouped and attacked from the northeast.

The activist-run Palmyra Coordination group said IS also advanced from the northwest, seizing a neighborhood on the outskirts and the Palmyra castle. The IS media arm Aamaq also said the militants had seized the castle.

The Syrian state news agency reported that army units backed by Russian air power had clashed with the IS militants late Saturday on three fronts, foiling an attack.

Palmyra is home to towering 2,000-year-old ruins and was a major tourist attraction before the civil war broke out in 2011. IS seized the town last year and held it for 10 months before being driven out by Russian-backed Syrian forces in March.

The militants have advanced on Palmyra in recent days, with reports of heavy fighting within the town itself. Syria's army has been largely focused on the northern city of Aleppo, where it is waging a major offensive against Syrian rebels.