Air carrier Captain reported a position error during takeoff on the runway at Hanoi airport and rejected the takeoff. Reporter stated that GPS jamming may have contributed to the error.

Narrative

Received a FMC RUNWAY DISAGREE when takeoff power was set. Rejected takeoff.We were cleared for takeoff on runway 11R. 11R was loaded in the FMC with the appropriate SID. Runway 11R was verified. Aircraft control was passed to the FO; pilot flying; throttles advanced and thrust set. Audible and visible alerts of FMC DISAGREE occurred at low speed; I took the airplane; rejected the takeoff and exited the runway on S3. We ran checklists; discussed the issues. RUNWAY Position was an active EICAS alert; with associated checklist. We addressed it after running the REJECTED TAKEOFF checklist. Our decision was to takeoff; which happened uneventfully. Condition: RAAS (Runway Awareness and Advisory System) position data is lost. The condition may be temporary.NOTE: RAAS voice annunciations and alerts are not available. Ground proximity alerts that occur are valid.The Condition was displayed on the checklist. Cause: We had the correct runway in the FMC; 11R; but we received the FMC RUNWAY DISAGREE when takeoff power was set. The cause could be internal such as a database error; or external such as GPS problems. After the reject and after taxiing clear of the runway and running the rejected takeoff checklist; we received a RUNWAY POS on EICAS. Therefore; I conclude the event was caused by a faulty RUNWAY Position; but I don't know why. Discussion with a supervisor lead to an investigation of the database to see if it is in error; and a discussion of possible GPS jamming was held.Suggestions: Threat awareness and detection as described in the FOM and good crew communication provided the ability to safely handle the issue. Prevention of such instances isn't possible; we must be prepared for anomalies and determine if we have reliable systems to continue; while using standard company procedures; guidance; and training.