The national prosecutor's office said today that it had asked the Internal Security Agency, a counterterrorism body, to verify media reports of the alleged death.
SITE Intelligence Group, which monitors jihadi postings online, reported Wednesday that the man, using the name Abu Khattab al-Polandi, was killed. It cited IS in Aleppo province.
The prosecutor's office said the man has been under investigation in Poland for "crimes of a terrorist nature" and illegal firearms possession. An international arrest warrant was issued for him last year.