Story highlights The militants seized control of Palmyra in May 2015

Syrian army forces and militias chased out ISIS in March

(CNN) ISIS is reportedly making inroads in the central Syrian city of Palmyra -- nearly a year after government forces recaptured the ancient city from the terror group, according to the activist-run Palmyra Coordination Committee.

The activists reported on social media Saturday that ISIS had taken control of neighborhoods in northern and northwestern parts of the city known for some of the world's most treasured ruins.

Intense fighting on the city's outskirts Saturday afternoon forced the withdrawal of hundreds of Syrian troops and Shiite militias, according to the Palmyra Coordination Committee.

CNN has not been able to confirm the developments that appeared on the activists' social media postings.

The development could be a huge setback for Syrian forces and militias loyal to the government who recaptured Palmyra from ISIS in late March, state-run media reported.

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