Activists and officials say Islamic State fighters are combing Palmyra, detaining and killing dozens of people two days after seizing the historic Syrian town.

Homs-based activist Bebars al-Talawy and an opposition Facebook page say that as many as 280 soldiers and pro-government forces have been killed in Palmyra since it was captured Wednesday.

The Britain-based Syrian Observatory for Human Rights says IS fighters have killed 17 men and that it has unconfirmed reports of the killing of "tens" more.

Gov. Talal Barazi of the central province of Homs, which includes Palmyra, said Friday that IS fighters have abducted men and "might have committed massacres."

The ISIS group has massacred hundreds of Syrian and Iraqi soldiers following past conquests, often boasting about the killings online.