British Police Launch Major Counter-Terror Drill

British police on Tuesday launched a major counter-terror exercise in London partly influenced by the Charlie Hebdo attacks in Paris in January, just days after an Islamist gun massacre in Tunisia.

The exercise including all emergency services also comes ahead of the 10th anniversary commemorations of the July 7, 2005 attacks on London's transport system, when four suicide bombers killed 52 people.

"We are taking part in a 999 exercise today which will test the emergency services' response to a marauding terrorist attack in London," the police force tweeted.

The exercise, codenamed "Operation Strong Tower", was being held in a disused London Underground station at Aldwych in the West End theater district.

Officers said that much of the exercise would be held out of public view but warned that passersby might hear loud noises and see streets cordoned off.

"If you are out & about near the Strand today -- there is a 999 exercise happening close by -- not a real incident," the police tweeted.

A total of 1,000 people including emergency medical services and transport workers will be involved in the drill, which will continue on Wednesday.

The police said the exercise was also partly influenced by the hostage-taking in Sydney in December when two hostages died in a 16-hour siege at a cafe that had been taken over by a gunman.

"Sadly, London is no stranger to terrorism. Given the changing nature of the very real terrorism threat and events around the world we need to constantly adapt our plans," Maxine de Brunner, a deputy assistant commissioner in London's police force, said in a statement.

The exercise has been planned for six months and officers emphasized that there was no link to the Islamist massacre on Friday in which a Kalashnikov-toting gunman mowed down 38 tourists at a seaside resort near Sousse in Tunisia.

Eighteen British victims have been identified so far and officials estimate that the death toll will rise to "around 30" in the worst loss of British lives in a terror attack since the 2005 bombings.