A teenager was killed when an explosive device he was carrying detonated prematurely as he attempted to stage an attack in Bahrain, authorities said.

The tense Gulf state has expanded crackdowns on so-called "terrorist" cells suspected of bombings targeting security forces and others in the strategic kingdom, which is home to the US Navy's 5th Fleet.

The Sunni-ruled nation has been locked in non-stop unrest since an uprising by the country's Shiite majority began in early 2011.

The official Bahrain News Agency said a gun and ammunition were found near the body of the 17-year-old boy about 10km west of the capital, Manama.

Authorities said the youth was wanted in connection with previous attacks.

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