Bahraini opposition groups claimed on Saturday that a man was killed during clashes with security forces, threatening to sharply escalate the Gulf nation's unrest as officials struggle under the world spotlight as hosts of the Formula One Grand Prix. Authorities opened an investigation in a bid to defuse tensions.

At least 50 people have died in the unrest since February 2011 in the longest-running street battles of the Arab Spring. Bahrain's Shia majority seeks to break the near monopoly on power by the ruling Sunni dynasty, which has close ties to the West.

Persistent protests have left the country's rulers struggling to keep attention on the build-up to Sunday's Formula One race — Bahrain's premier international event. It was called off last year amid security fears and Bahrain's leaders lobbied hard to hold this year's event in efforts to portray stability and mend the country's international image.

A statement by Bahrain's Interior Ministry said a probe was under way, but gave no other immediate details. The death, however, was likely to intensify a wave of expected protests to coincide with the F1. The body was found in an area west of the capital Manama, where clashes broke out after a massive protest march on Friday.

Opposition factions said riot police and demonstrators were engaged in running skirmishes around the village of Shakhura, about eight km west of the capital Manama and known for its burial mounds dating back more than 5,000 years.

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