Air carrier First Officer reported at the gate before push back and during taxi; GPS jamming at LTFM; Istanbul Airport; Turkey.

Narrative

Operating scheduled pairing IST-ZZZZ. Pre-flight normal until cockpit setup--noticed no GPS updating on ND (Navigation Display)/FMC during FO pre-flight. We were briefed by jumpseater who operated flight inbound to IST that they experienced significant GPS jamming/spoofing; so we attributed the lack of signal to that (common in this region). Also parked near a large metal building; we leveraged our experience and came to conclusion that could also be interfering with a good GPS signal.We continued through pushback with no EICAS alerts and no other anomalies aside from lack of GPS updating. Our game plan was given the likely jamming environment/possible interference; that as we taxied out toward runway that we would receive better GPS signal/updating. However; on taxi out; our ANP began to decline; first slowly; and then significantly due to inertial only. We tried manipulating FMS; toggling GPS updating ON/OFF; as well as attempting radio updates--ANP continued to decline down on the taxi; eventually resulting in 'RNP Unable.' With continued troubleshooting as we approached the hold short; I grew exceedingly more uncomfortable with the situation; as it also appeared our inertial position was vastly different from what our GPS was showing (several miles). In our last effort to continue troubleshooting; we were given 'line up and wait clearance' and during the runway verification; Captain and I looked at each other; pointed to the disparity in position on the ND; and came to the easy conclusion that we were not comfortable with this. Before receiving takeoff clearance we told the Tower we needed to taxi clear the runway for further troubleshooting.Ultimately; we could not resolve on our own using any Emergency Checklist and resulted in block turn back. We got on SATCOM with Dispatch/Maintenance Control who advised us to pull 3 circuit breakers. After reset; it took a few moments; but GPS updating displayed on ND; and the situation seemed resolved. Followed remaining maintenance process; awaited signoff; and proceeded on leg. No further GPS jamming/signal interference occurred for the remainder of the flight; which was uneventful. While we maintained a 'go-oriented' mindset; if I could do anything differently; it would have been arguably more prudent to be a bit more assertive earlier in stating I wasn't comfortable with the degrading ANP and never continued toward the runway. Cause: Curious if perhaps inbound crew did something to the jet during GPS jamming that resulted in us not being able to do so. Suggestions: Wonder if perhaps after experiencing GPS jamming/spoofing if an AML (Aircraft Maintenance Logbook) write up should be required. Ultimately a power down or CBs (circuit breakers) being pulled fixed the issue; so curious if this should be done following jamming.