TAIPEI >> China’s military has sailed and flown closer to Taiwan in recent weeks than it has before, and staged mock attacks on foreign vessels ahead of the inauguration of the island’s next president on Monday, according to Taiwanese government reports.

Taiwan will inaugurate its new president, Lai Ching-te, as Beijing ramps up military and political pressure to assert its sovereignty over democratically governed Taiwan — a claim Taipei strongly rejects.

Since late April an increasing number of Chinese military planes and vessels have staged drills that have alarmed Taiwan, including close approaches to the island’s contiguous zone, which is 24 nautical miles (44 km) off its coast, according to two Taiwan officials and internal reports reviewed by Reuters.

Taiwan had anticipated intensified Chinese military activity, Deputy Defence Minister Po Horng-huei told reporters last week. Reuters reported exclusively on Monday that Taiwan and the U.S. Navy held unpublicized drills in April.

On Tuesday evening, 15 Chinese planes, including Su-30 jets, crossed the median line and entered Taiwan’s air defense identification zone, carrying out “joint combat readiness patrols” in conjunction with warships, according to Taiwan’s defense ministry.

Some of the planes simulated attacks on foreign vessels entering the southern Taiwan Strait or the Bashi Channel that separates Taiwan from the Philippines, said one of them, a senior security official, citing intelligence gathered by Taiwan.

“They are like flies buzzing us every day,” the official said, noting changes in the flight patterns, scale and frequency.

China’s defense ministry and its Taiwan Affairs Office did not respond to requests for comment.

On May 11-12, about 10 Chinese vessels, including frigates and coast guard boats, were spotted near Taiwan and some approached Taiwan’s contiguous zone, according to the government reports.

China usually dispatches only four or so ships at a time near to the island, the two Taiwan officials told Reuters. Both declined to be named because of the sensitivity of the matter.

“Since late April they have become more and more provocative,” the senior security official said.

Dozens of Chinese fighter jets, including J-16s and J-10s, have crossed the median line of the Taiwan Strait since late April, and some circled near Taiwan’s contiguous zone; they were tracked by air defense radars and driven away by Taiwanese aircraft, the government reports show.

Taiwan’s defense ministry referred Reuters to comments it made at a news conference this week, during which officials said Taiwan has a “full grasp” of the situation.

“The national military is not the troublemaker of the Taiwan Strait. We will not engage in any provocation, and we must make it clear that any provocative behaviour is unhelpful to regional peace and stability,” said defense ministry spokesman Sun Li-fang.

China has for years staged almost daily incursions into Taiwan’s air defense identification zone, including fighter jets briefly crossing the median line, the strait’s unofficial boundary, which Beijing says does not exist.

Taiwan’s defense ministry releases daily reports on Chinese military activities near Taiwan but does not disclose detailed information.

Lai is particularly disliked by Beijing, which views him as a “dangerous separatist” and has rebuffed Lai’s repeated offers of talks with China. He has been vice president for the past four years and will take over from President Tsai Ing-wen.

On Tuesday, Lai again offered talks with Beijing and vowed to safeguard peace across the strait.

“The irony is that when the new president vowed to ensure the status quo, Beijing responded with destroying the status quo,” the senior security official said.