Prime Minister Theresa May has condemned the "horrifying" terror attack in Nice which has killed at least 84 people, including several children.
She also said the Government "are working urgently to establish whether any British nationals were caught up in the attack".
Mrs May added: "If, as we fear, this was a terrorist attack then we must redouble our efforts to defeat these brutal murderers who want to destroy our way of life."
She also confirmed she would be speaking to French President Francois Hollande today "and make clear that the United Kingdom stands shoulder to shoulder with France today as we have done so often in the past."
French Prime Minister Manuel Valls faced boos and calls to resign as he laid a wreath for the 84 people killed in the lorry attack in Nice.
Hours later Mohamed Lahouaiej Bouhlel drove a 19-tonne lorry down the promenade killing 84 people and injuring 200 more.
France's prime minister stated on Sunday he believed the man behind the Nice lorry attack was radicalised "very quickly"