In the wake of the terrorist attacks that killed more than 120 people in Paris late Friday, British Prime Minister David Cameron said the threat level in the U.K. remained “severe” and likely would stay there for a while, Reuters reported Saturday. Cameron condemned the attacks and conducted a meeting of an emergency response committee in London.

The current “severe” threat level means an attack is highly likely. The highest threat level in Britain is “critical,” but Cameron said he had no plan move it there, according to the Telegraph in the U.K. The “severe” threat level has been in place since August 2014, Reuters said.

Referring to the attacks in France, Cameron said, "We must be prepared for a number of British casualties.” And speaking directly to the French people, the U.K.'s prime minister said, "Your values are our values, your pain is our pain, your fight is our fight."

Security at major events and ports was strengthened across Britain Saturday. U.K. citizens in Paris were urged to stay indoors as well, the Daily Mail reported.

“The events in Paris are the worst acts of violence in France since the Second World War, the worst terrorist attack in Europe for a decade, a horrifying and sickening attack,” the Mail quoted Cameron as saying.

Police evacuated a terminal at Gatwick, Britain’s second-busiest airport, after police saw a suspicious man discarding something there. Meanwhile, police are expected to be heavily patrolling London’s theater district, the West End, Saturday night, according to Reuters.

The Islamic State group, formerly known as either ISIL or ISIS, has claimed responsibility for the coordinated Paris terror attacks, which French President Francois Hollande has blamed on terrorism.