LONDON - The British government is conducting a survey of its soldiers to determine if those exposed to powerful explosions in Iraq and Afghanistan have suffered mild traumatic brain injuries, the Ministry of Defense said Saturday.

The ministry said it has begun distributing questionnaires to British troops in both countries as part of a self-assessment program to see if they have symptoms such as memory loss, depression and anxiety.

The Guardian newspaper, which first reported the survey, said it followed concerns within the U.S. Army that up to 20 percent of its returning soldiers and Marines were suffering from these conditions.

The newspaper said Saturday that the condition has been designated by the Pentagon as one of the four "signature injuries" of the Iraq war. Powerful roadside bombs targeting U.S. and British convoys are one of the main risks that soldiers face in Iraq and Afghanistan.

A spokesman for Britain's Ministry of Defense said Saturday that it was working alongside a U.S. investigation of the condition, in part to determine how widespread it may be.

"It is a very, very complex area. We have no way of knowing whether that (the U.S. assessment) is accurate because there is a level of dispute as to what constitutes mTBI," or mild traumatic brain injury, the spokesman said, speaking on condition of anonymity in keeping with ministry regulations.

The spokesman said mTBI's symptoms may last for as little as 72 hours, and can disappear entirely within several weeks or months.

The condition, which also is associated with contact sports such as rugby and boxing, can occur when a soldier suffers a blow to the head or is near an explosion.