TAIPEI, Aug 2 (Reuters) - Taiwan's defence ministry has 'reinforced' its combat alertness level from Tuesday morning to Thursday noon, the island's official central news agency reported, citing unidentified sources.

U.S. House of Representatives Speaker Nancy Pelosi was set to visit Taiwan on Tuesday, three sources said, as the United States said it wouldn't be intimidated by Chinese threats to never "sit idly by" if she made the trip to the self-ruled island claimed by Beijing.