BEIJING — China announced on Thursday that it would establish its first overseas military outpost and unveiled a sweeping plan to reorganize its military into a more agile force capable of projecting power abroad.

The outpost, in the East African nation of Djibouti, breaks with Beijing’s longstanding policy against emulating the United States in building military facilities abroad.

The Foreign Ministry refrained from describing the new installation as a military base, saying it would be used to resupply Chinese Navy ships that have been participating in United Nations antipiracy missions.

Yet by establishing an outpost in the Horn of Africa — more than 4,800 miles away from Beijing and near some of the world’s most volatile regions — President Xi Jinping is leading the military beyond its historical focus on protecting the nation’s borders.