British citizens may be among the 120 or more people killed in a wave of terrorist violence in Paris overnight, Prime Minister David Cameron said in a statement as he offered condolences and help to France.
The PM said Britain and France would stand together in the face of this tragedy and pledged to redouble the effort to eradicate extremist ideology.
“Together with our friends and allies around the world we will stand up for all we believe in,” he said.
Cameron was speaking after a meeting of a government committee responsible for responding to threats and emergencies, known as Cobra, to discuss the terrorist attacks in Paris and the UK's next move.
London Metropolitan Police's Assistant Commissioner Mark Rowley told the BBC that policing across the country would be strengthened in the wake of the French tragedy.
A spokesman for the Met said that additional police patrols would be deployed across London's popular West End theater and restaurant district.
The UK remains at its second-highest “severe” terrorism threat level since August 2014, which means the risk of attack is considered highly likely.
The attacks in France left at least 120 people killed. Eight perpetrators were reported killed in firefights with security troops. The French government put the country on lock down and declared a state of emergency in response.