Air carrier Captain reported GPS jamming while flying through Ankara's airspace just south of Ukrainian airspace which caused the aircraft to turn toward Ukrainian airspace. Captain avoided the airspace and notified ATC.

Narrative

While flying through Ankaras airspace just south of Ukrainian airspace we were experiencing GPS jamming. We were navigating on the IRS with DME DME updating. I had the POS REF page displayed on my Control Display Unit (CDU) to monitor the RNP/ANP. We had normal indications as RNP 1.0 and ANP 0.38. After passing position ODERO on track to position LUGEB with Sofia Control the aircraft began a a right turn (towards Ukrainian airspace) and we immediately noticed that even though we were on the correct track; the ANP rapidly was increasing from 0.38 to 22.0 in a matter of seconds. We received a CDU scratch pad message to verify position as well as the expected EICAS message unable RNP. I immediately selected HDG select and we notified ATC we suspected spoofing and requested a heading. Thankfully we never deviated from our track. We flew the assigned heading and ATC asked us to advise when we had GPS available again. The suspected spoofing lasted approximately 3 to 4 minutes and then the ANP rapidly returned to 0.38. Shortly after the GPS jamming ended we advised ATC. We were then able to navigate normally in LNAV. The remainder of the flight was uneventful.