VLBI observations of the galactic center source SGR A* at 86 GHz and 215 GHz

We have observed and detected Sgr A* with VLBI at 86 GHz and at 215 GHz in March 1995. At 86 GHz the measured closure phase is close to zero, consistent with a point-like or symmetric structure of 190 +/- 30 mu as in size. At 215 GHz we have detected Sgr A* with a signal-to-noise ratio of 6. This yields a tentative size estimate of 110 +/- 60 mu as which, despite of a limited calibration accuracy and uncertainty in the origin of the mm/sub-mm total flux density excess, lies well above the scattering size of 20 mu as at this frequency. The intrinsic size of Sgr A* thus appears to be 17 +/- 9 Schwarzschild radii for a 2.6 * 10^6 M_solar black hole.