A tamper-proof electronic security seal which includes a bolt and a locking element and an electronic seal element. The bolt has a head and a hollow shank extending therefrom having a longitudinal bore formed therein. The shank is dimensioned to pass through a lock hasp and has a free end formed for locking engagement with the locking element. The electronic seal element is formed for mechanical connection to the bolt head, and includes an electrical power source, a control unit, communications means responsive to the control unit and a sensor adapted for insertion into the longitudinal bore of the shank, and connected to the control unit. In response to a severing of the shank and the sensor inserted therein, the control unit is operative to activate the communications means to emit an alarm signal.