BEIJING (AP) — Recent Chinese air and sea drills simulating an encirclement of Taiwan were intended as a “serious warning” to pro-independence politicians on the self-governing island and their foreign supporters, China said Wednesday, as signs emerged that Beijing will take further action.

The three days of large-scale air and sea exercises named Joint Sword that ended Monday were a response to Taiwanese President Tsai Ing-wen’s meeting with U.S. House Speaker Kevin McCarthy in California last week during a transit visit to the U.S. China had warned of serious consequences if that meeting went ahead.

Although China said the exercises are over, it has kept up military pressure against Taiwan in the past few days and signaled it will do more.

Taiwan’s Ministry of Transportation said Wednesday it had received a notice from China’s Civil Aviation Administration that it would set up a control zone to “restrict flights” in parts of northern Taiwan from April 16-18, in effect setting up an area where flights would not be allowed to go.

“On their own, they set up a warning area to control flights within our country’s jurisdiction’s Taipei Aviation Information Region, using the excuse of aerospace activities,” the Taiwan statement said.

Taiwan said it strongly protested the notice and was able to get China to reduce the flight ban time from three days to 27 minutes on the morning of April 16. It is unclear what China plans to do at that time. Taiwan’s Defense Ministry said it was looking into the matter but could not provide further details.

China claims Taiwan as its own territory to be brought under its control by force if necessary and regularly sends ships and warplanes into airspace and waters near the island. It defended its recent military actions Wednesday.

“The People’s Liberation Army recently organized and conducted a series of countermeasures in the Taiwan Strait and surrounding waters, which is a serious warning against the collusion and provocation of Taiwan independence separatist forces and external forces,” Zhu Fenglian, a spokesperson for the Cabinet’s Taiwan Affairs Office, said at a biweekly news conference.

“It is a necessary action to defend national sovereignty and territorial integrity,” she said.

Such missions have grown more frequent in recent years, accompanied by increasingly bellicose language from the administration of Communist Party leader Xi Jinping. Any conflict between the sides could draw in the U.S., Taiwan’s closest ally, which is required by law to consider all threats to the island as matters of “grave concern.”

On Wednesday, Taiwan’s Ministry of National Defense said it tracked 35 flights by People’s Liberation Army warplanes within the last 24 hours, and eight navy vessels in the waters surrounding the island.

“There are still some navy ships and airplanes carrying out harassment in the area. We strongly condemn these deliberately threatening and provocative actions that destroy the regional peace and stability,” Sun Li-fang, a spokesperson for Taiwan’s Defense Ministry, said at a press briefing Wednesday.

The vast majority of Taiwanese favor maintaining their current de-facto independent status, while Tsai has said there is no need for a formal declaration since the island democracy is already an independent nation.

Despite that, China, which does not recognize Taiwan’s government institutions and has cut off contact with Tsai’s administration, routinely accuses her of plotting formal independence with outside backing — generally seen as referring to the U.S.

“External forces are intensifying their endeavor of containing China with Taiwan as a tool,” Zhu said.

Zhu also repeated China’s assertion that its military threats are “targeted at Taiwan’s independence separatist activities and interference from external forces, and by no means at our compatriots in Taiwan.”

What that means in practical terms isn’t clear, although Beijing has long exploited political divisions within Taiwanese society, which boasts a robust democracy and strong civil liberties.

“Taiwanese compatriots should clearly recognize the serious harm that the provocation of Taiwan independence forces poses to cross-strait relations and peace and stability in the Taiwan Strait, recognize the interests, distinguish right from wrong, and stand on the correct side of history,” Zhu said.

The Chinese military issued a threat as it concluded the exercises, saying its troops “can fight at any time to resolutely smash any form of ‘Taiwan independence’ and foreign interference attempts.”

In August, after then-Speaker Nancy Pelosi visited Taiwan, China conducted missile strikes on targets in the seas around Taiwan and sent warships and warplanes over the median line of the Taiwan Strait. It also fired missiles over the island that landed in Japan’s exclusive economic zone in a significant escalation.

The most recent exercises focused more on air strength, with Taiwan reporting more than 200 flights by Chinese warplanes. On Monday alone, Taiwan’s Defense Ministry tracked 91 flights by Chinese warplanes.

They also featured the use of China’s first indigenously built aircraft carrier, Shandong, which launched dozens of J-15 Flying Shark fighter missions during the exercises, according to Japanese officials.

Taiwanese military officials said they noted the Shandong’s appearance in the Pacific Ocean, to Taiwan’s east, and that it was the focus of their discussions and preparedness plans.

“Everyone can see clearly China’s ability to cross the first island chain is gradually improving. The so-called ‘anti-access/area denial’ ability is gradually improving,” said Lt. Gen. Li Tian-long at a press briefing Wednesday, referring to a military concept where forces prevent an adversary from entering a specific area.

Defense experts said China would likely use the Shandong to try to prevent foreign militaries from accessing that area based on its exercise movements.

Taiwan will launch an annual large-scale drill on Thursday jointly with its disaster services and Defense Ministry, as well as local governments. Last year, the government revamped the disaster-preparedness drills to include more wartime scenarios. This year, they said, that trend would continue with war-preparedness to comprise 70% of the drills’ contents.

The developments come as the USS Nimitz Carrier group is operating in the South China Sea south of Taiwan and as American and Filipino forces hold their largest combat exercises in decades in Philippine waters across the disputed South China Sea and the Taiwan Strait.

—-

AP reporter Huizhong Wu contributed to this report from Taipei, Taiwan.