A long-range acoustic device that can be used as a sonic weapon is to be deployed at the London Olympic Games starting in July, Britain's defence ministry said Saturday.

The US-built device can be used either as a powerful loudspeaker or to emit directional, pain-inducing sounds up to 150 decibels, a function that has been used against Somali pirates and for crowd control in Iraq.

The ministry said the device was among a "broad range of assets" to be in place during the Games, and would be mainly used in loud-hailer mode to issue verbal warnings to any boats causing concern on the River Thames.

Users of the most advanced model can "issue clear, authoritative verbal commands, followed with powerful deterrent tones to enhance response capabilities," projecting voices for up to 8,900 metres (5.7 miles), according to the website of LRAD Corporation, which makes the device.

It forms part of a security operation that is also set to include six missile batteries, Britain's largest warship -- the amphibious assault ship HMS Ocean, equipped with military helicopters -- and Typhoon fighter jets.

A security force of more than 40,000, backed by a huge intelligence operation, will guard venues, athletes and the millions of visitors expected to throng the British capital for the Games, which start on July 27.

"Lone wolf" terrorist attacks are a major concern, but a range of other threats are also being considered.