According to recent sources, China has increased its warnings to the US on a trip to Taiwan that House Speaker Nancy Pelosi has scheduled for August, even hinting at a potential military response.

The Financial Times initially reported on Sunday that six people familiar with the confidential letter to the Biden administration said it was much more threatening than past warnings Beijing has made about US relations with Taiwan.

The Financial Times said that the warning indicated a potential military reaction.

The US has maintained a policy of strategic ambiguity, accepting Beijing’s claim but not embracing it, despite the fact that China has long argued that Taiwan is a part of its territory.

The claim was confirmed on Monday by the spokeswoman for China’s foreign ministry.

At a routine press briefing, spokeswoman Zhao Lijian responded to questions regarding the report’s details by saying, “We are seriously prepared.”

Zhao responded when asked if China was “seriously prepared for” a military or diplomatic reaction, saying that if the US side was determined to go in its own manner, China will take strong steps to forcefully resist and respond.

China has not made clear what precise measures it would take, but there has been talk that it may launch another round of menacing military drills or even try to stop Pelosi’s plane from landing by establishing a no-fly zone over Taiwan.

Both the State Department and the White House National Security Council declined to comment on the story.

China has increased its military presence in the area of Taiwan in an effort to put pressure on the democratically elected administration there to recognize Chinese sovereignty.

The government of Taiwan claims that only the 23 million residents of the island can decide its destiny and that, despite its desire for peace, it will defend itself if attacked.

The island’s military was conducting its yearly multi-day exercises, involving combined air and sea exercises as well as the deployment of tanks and personnel, on Monday in Taipei, the capital of Taiwan, against the backdrop of growing tensions.

Police in Taipei told people to seek cover after a siren sounded just after midday. Shops shuttered, and streets were empty.

By the end of the month, according to Biden, he wants to talk with Xi Jinping, the president of China.