BEIJING—China has begun operating a homegrown satellite-navigation service that is designed to provide an alternative to the U.S. Global Positioning System and, according to defense experts, could help the Chinese military identify, track and strike U.S. ships in the region in the event of armed conflict.

The Beidou Navigation Satellite System started providing initial positioning, navigation and timing services to China and its "surrounding areas" on Tuesday, Ran Chengqi, a spokesman for the system, told a news conference.

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