The U.S. security company, Mandiant, identified the People’s Liberation Army’s Shanghai-based Unit 61398 as the most likely driving force behind the hacking. Mandiant said it believed the unit had carried out “sustained” attacks on a wide range of industries.

The hacking dispute adds to diplomatic tension between China and the United States, already strained by Chinese suspicion about Washington’s “pivot” back to Asia and arguments over issues from trade to human rights.

(Reporting by Ben Blanchard; Editing by Robert Birsel)