At least one Briton has been injured in the terrorist attack in Nice, new Foreign Secretary Boris Johnson said.
"The only information I have is that there is one UK national who is injured but it is still too early to say at the moment," Johnson said.
He described the attack as "appalling" and said it represented the "continuing threat" to Europe from terrorism.
He confirmed there would be meetings later to discuss the implications for the UK and that he would speak to his French counterpart.
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"