Boris Johnson has said he is “appalled” to hear of the “barbaric” suspected terror attack at a church in France in which three people were killed.
A suspect was arrested after the Thursday morning knife attack at the Notre Dame church in Nice and was taken to a nearby hospital after being injured as he was detained.
He was believed to be acting alone and police are not searching for other attackers, an official said.
The anti-terrorism prosecutor’s office said an investigation has been opened into an attack with a terrorist connection.
In a post on Twitter, the Prime Minister said: “I am appalled to hear the news from Nice this morning of a barbaric attack at the Notre-Dame Basilica.
“Our thoughts are with the victims and their families, and the UK stands steadfastly with France against terror and intolerance.”
Images by French media showed the neighbourhood locked down and surrounded by police and emergency vehicles. The killings took place less than half a mile from the site where another attacker drove a truck into a Bastille Day crowd in 2016, killing dozens.
Sounds of explosions could be heard as sappers exploded suspicious objects.
Nice’s mayor Christian Estrosi said the attacker shouted “Allahu akbar!” repeatedly as police apprehended him and that “the meaning of his gesture left no doubt”.
Speaking to reporters, Mr Estrosi said two people were killed inside the church and in a tweet added that the church caretaker was among those attacked at the Notre Dame Basilica.
Home Secretary Priti Patel, speaking during a visit to Essex Police headquarters, said: “This is absolutely terrible and we are devastated for the people of France with the news that we are hearing so far.
“Clearly we need to find out much more information and this is early stages and of course we will speak to our colleagues in France. I will speak to my counterpart later today.
“But at this particular stage all our thoughts are with the people of France and obviously those that have lost their lives today as well.
“And we stand ready to provide any support that the French government needs at this really crucial time.”
Meanwhile Foreign Secretary Dominic Raab said: “The UK stands with France today in sorrow, shock and solidarity at the horrifying events in Nice.
“Our thoughts are with the victims and their families and we offer every support to the French people in pursuing those responsible for this appalling attack.”
The exact motive of the attack was unclear but comes as France is under alert for Islamic extremist acts amid tensions over two other recent attacks in France with links to caricatures of the Prophet Mohammed.
Less than two weeks ago, an attacker decapitated a French middle school teacher who showed caricatures of the Prophet Mohammed for a class on free speech. Those caricatures were published by Charlie Hebdo and cited by the men who gunned down the newspaper’s editorial meeting in 2015.
In September a man who had sought asylum in France attacked bystanders outside Charlie Hebdo’s former offices with a butcher knife.