At a voir dire examination, a challenged juror may be examined as a witness to prove or disprove the challenge. The juror shall answer every question pertinent to the inquiry. When challenged on the ground that the juror is not a citizen of the United States, the juror's own testimony is competent evidence of the fact of naturalization, without other evidence. The juror's testimony on the issue of citizenship may be disputed by the challenger. At a voir dire examination either party may examine other witnesses on either side. The Rules of Evidence applicable to the trial of other issues govern the admission or exclusion of testimony at a voir dire examination.