LONDON (AP) — British police in inflatable powerboats have boarded a River Thames cruise boat as part of an exercise simulating the hijacking of a tourist vessel in London.

The Metropolitan Police force says Sunday's training exercise is 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.