BEIJING, China (AP) — China said Monday it is extending threatening military exercises surrounding Taiwan that have disrupted shipping and air traffic and substantially raised concerns about the potential for conflict in a region crucial to global trade.

The announcement further increases uncertainty in the crisis that developed last week with US House Speaker Nancy Pelosi’s visit to Taiwan.

The exercises include anti-submarine drills, apparently targeting US support for Taiwan in the event of a potential Chinese invasion according to social media posts from the eastern leadership of China’s ruling Communist Party’s military arm, the People’s Liberation Army.

China claims Taiwan as its own territory, and its leader Xi Jinping has focused on bringing the self-governing island democracy under the mainland’s control, by force if necessary. The two sides split in 1949 after a civil war but Beijing considers visits to Taiwan by foreign officials as recognising its sovereignty.

Xi is seeking a third term as Communist Party leader later this year. His control over the armed forces and what he has defined as China’s “core interests” — including Taiwan, territorial claims in the South China Sea and historic adversary Japan — are key to maintaining his nationalist credentials.

The military has said the exercises, involving missile strikes, warplanes and ship movements crossing the midline of the Taiwan Strait dividing the sides, are a response to Pelosi’s visit.

China has ignored calls to calm the tensions, and there was no immediate indication of when it would end what amounts to a blockade.

On Monday, Chinese Foreign Affairs Ministry spokesperson Wang Wenbin said China would “firmly safeguard China’s sovereignty and territorial integrity, resolutely deter the US from containing China with the Taiwan issue, and resolutely shatter the Taiwan authorities’ illusion of ‘relying on the US for independence’ “.

Asked in Dover, Delaware, on Monday about China’s response to Pelosi’s visit, US President Joe Biden said: “I’m not worried but I’m concerned they’re moving as much as they are. But, I don’t think they’re going to do anything more than they are.”

China’s slowing economic growth, which has reduced options among migrant workers as well as college graduates, has raised the spectre of social unrest. The party has maintained its power through total control of the press and social media, along with suppression of political opponents, independent lawyers, and activists working on issues from online free speech to LGBTQ rights.

China doesn’t allow public opinion polls, and popular opinion is hard to judge. However, it generally skews in favour of the Government and its efforts to restore China’s former dominant role in the region, which puts it in conflict with the United States and its allies including Japan and Australia.

Taiwan’s defence ministry said Sunday it detected a total of 66 aircraft and 14 warships conducting the naval and air exercises. The island has responded by putting its military on alert and deploying ships, planes and other assets to monitor Chinese aircraft, ships and drones that are “simulating attacks on the island of Taiwan and our ships at sea”.

Meanwhile, Taiwan’s official Central News Agency reported that Taiwan’s army will conduct live-fire artillery drills in southern Pingtung county on Tuesday and Thursday, in response to the Chinese exercises.

The drills will include snipers, combat vehicles, armoured vehicles as well as attack helicopters, read the report which cited an anonymous source.