China’s military flew 38 fighter jets and other warplanes near Taiwan, the Taiwanese defense ministry said Friday, in the biggest such flight display since the large military exercise in which it simulated sealing off the island earlier in April.

Naval vessels were also seen in the area as part of China’s long-running campaign of intimidation against Taiwan.

Later Friday, China’s People’s Liberation Army issued a protest over the flight of a United States Navy P-8A Poseidon anti-submarine patrol aircraft through the Taiwan Strait, which separates mainland China from the self-governing island democracy claimed by Beijing.

Calling Thursday’s flight a provocation that the U.S. “openly hyped up,” the PLA’s Eastern Theater Command said it scrambled fighter jets to monitor the plane’s flight.

Such acts “fully prove that the U.S. is a disruptor of peace and stability in the Taiwan Strait and a creator of security risks,” the statement said. “Theater troops maintain a high level of alert at all times and resolutely defend national sovereignty and security as well as regional peace and stability.”

The U.S. 7th Fleet said Thursday’s flight was in accordance with international law and “demonstrates the United States’ commitment to a free and open Indo-Pacific.”

“The United States will continue to fly, sail, and operate anywhere international law allows including within the Taiwan Strait,” the statement said.

The U.S. remains Taiwan’s closest military and political ally, despite the lack of formal diplomatic ties between them. U.S. law requires Washington to treat all threats to the island as matters of “grave concern,” though it remains ambiguous over whether American forces would be dispatched to help defend the island.

Beijing has threatened to bring Taiwan under its control by force if necessary, and China’s intensely nationalistic leader Xi Jinping has sworn never to give up “a single inch” of territory claimed by his country — a pledge that applies to Taiwan, the disputed border with India, and the South China Sea that China claims almost in its entirety.

In addition to the latest Chinese warplane flights, Chinese navy vessels were spotted in the area from 6 a.m. Thursday to 6 a.m. Friday, the island’s Defense Ministry said.

Nineteen of the aircraft flew across the midline in the Taiwan Strait that separates the island from the mainland, the ministry said. It said they included five SU-30 and two J-16 fighter jets, along with one drone: a large, long-endurance TB-001 Scorpion capable of carrying a variety of bombs and missiles that circled the island in a relatively rare move, according to a diagram from the Defense Ministry.

It wasn’t clear what, if anything, prompted the large-scale Chinese action, but China’s efforts to train for a potential attack, wear down the island’s military and impact Taiwan’s politics have become increasingly ambitious.

U.S. military officials recently said they are increasingly concerned that a massive buildup in China’s military capabilities makes the potential for a conflict more likely.

China held exercises simulating the sealing off the island after the sensitive April 5 meeting between Taiwan’s President Tsai Ing-wen and U.S. House Speaker Kevin McCarthy in California. China opposes any exchanges at the official level between Taiwan and other governments.

Taiwan and China split in 1949 following a civil war that ended with the Communist Party in control of the mainland. The island has never been part of the People’s Republic of China, but Beijing says it must unite with the mainland, by force if necessary.

(AP)