China claims most of the energy-rich waters through which about $5 trillion in ship-borne trade passes every year. Neighbors Brunei, Malaysia, the Philippines, Taiwan and Vietnam also have claims.

Taiwan's claim to Itu Aba is complicated by the fact that China considers Taiwan sovereign territory. Taiwan and China both claim the South China Sea using old maps that date back to the late 1940s when the Nationalists ruled China.

The defeated Nationalists fled to Taiwan in 1949 after losing to Mao Zedong’s Communists. Taiwan has been self-ruled ever since.

Taiwan's coast guard said that the live-fire drills around Itu Aba were routine. The scheduled drills began on Wednesday and end on Friday.

Vietnamese Foreign Ministry spokesman Le Hai Binh said the drills were "a serious violation of Vietnam's sovereignty over the (Spratly) archipelago, threatening peace, stability, and maritime safety and security, stressing and complicating the situation in the East Sea (South China Sea)."

"Vietnam resolutely opposes (the drills) and asks Taiwan to not repeat similar actions," Binh said in a statement posted on the ministry website.

By Mai Nguyen & J.R. Wu - Reuters - March 30, 2017