China spent $21 billion on military exercises in the Taiwan Strait, the East and South China Seas and the Western Pacific last year, nearly 40% higher than in 2023, according to Taiwan government estimates based on its tracking of aircraft and ships and working out the cost of fuel and other expenses.

The internal research by Taiwan’s armed forces, reviewed by Reuters and corroborated by four Taiwan officials, offers rare details of where China’s defense spending is probably going as Beijing expands its military footprint and scope of its drills, alarming regional capitals and Washington.

China budgeted 1.67 trillion yuan ($233.47 billion) in defense spending for last year, but diplomats widely believe that number is under-reported. China does not give any breakdown on how the money is spent.

The officials, who were briefed on the research, declined to be identified because of the sensitivity of the matter.

Neither China’s defense ministry nor its Taiwan Affairs Office responded to requests for comment. China, which views Taiwan as its own territory over the objections of Taipei’s government, has repeatedly said its military spending is transparent and presents no threat.