British police in inflatable powerboats stormed a River Thames cruise boat Sunday as part of an exercise simulating the hijacking of a tourist vessel in London.

The Metropolitan Police force said Sunday's training exercise involving more than 200 officers was designed to test the emergency services' response to "a marauding terrorist attack."

It's the first such exercise to focus on the winding tidal river that carries large amounts of commuters, tourists and freight through the heart of London.

Last year a report commissioned by Mayor Sadiq Khan recommended strengthening security measures along the Thames.

Britain's official threat level from terrorism stands at "severe," meaning an attack is highly likely.

Police Commander B.J. Harrington said the exercise Sunday was not held in response to a specific threat. But he noted that deadly truck attacks last year in Nice and Berlin showed that methods of extremist attacks were evolving.

"And, of course, the river runs right the way through London, so why wouldn't we prepare for that?" Harrington said.