Belgian police are still hunting a gunman who shot dead two Israelis and a French woman at the Jewish Museum in Brussels, in an attack thought to be motivated by anti-Semitism.
Security around all Jewish institutions in Belgium was raised to the highest level following Saturday's shooting, while French authorities stepped up security after two Jews were attacked near a Paris synagogue.
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Michael Fallon has received reassurances from his US counterpart that security ties with Britain will "endure" following a vote for Brexit.
On Friday, police said it appeared the girl had shot herself in the face with the weapon.
The showers will be slow-moving, heavy and thundery at times, particularly in central and eastern areas.