U.S. House Speaker Nancy Pelosi arrived in Taiwan late Tuesday, becoming the highest-ranking American official in 25 years to visit the self-ruled island claimed by China, which quickly announced that it would conduct military maneuvers in retaliation for her presence.

Pelosi flew in aboard a U.S. Air Force passenger jet and was greeted on the tarmac at Taipei’s international airport by Taiwan's foreign minister and other Taiwanese and American officials. She posed for photos before her motorcade whisked her unseen into the parking garage of a hotel.

Her visit ratcheted up tension between China and the United States because China claims Taiwan as part of its territory, and it views visits by foreign government officials as recognition of the island’s sovereignty.

The Biden administration, and Pelosi, say the United States remains committed to the so-called one-China policy, which recognizes Beijing but allows informal relations and defense ties with Taipei.

The speaker framed the trip as part of a broader mission at a time when “the world faces a choice between autocracy and democracy.” Her visit comes after she led a congressional delegation to the Ukrainian capital of Kyiv in the spring, and it serves as a capstone to her many years of promoting democracy abroad.

"We must stand by Taiwan,” she said in an opinion piece published by The Washington Post on her arrival in Taiwan. She cited the commitment that the U.S. made to a democratic Taiwan under a 1979 law.

“It is essential that America and our allies make clear that we never give in to autocrats,” she wrote.

Taiwan and China split during a civil war in 1949, but China claims the island as its own territory and has not ruled out using military force to take it.

The Biden administration did not explicitly urge Pelosi to call off her plans. It repeatedly and publicly assured Beijing that the visit did not signal any change in U.S. policy toward Taiwan.

Soon after Pelosi’s arrival, China announced a series of military operations and drills, which followed promises of “resolute and strong measures” if Pelosi went through with her visit.

The People’s Liberation Army said the maneuvers would take place in the waters and skies near Taiwan and include the firing of long-range ammunition in the Taiwan Strait.

“This action is a solemn deterrent against the recent major escalation of the negative actions of the United States on the Taiwan issue, and a serious warning to the ‘Taiwan independence’ forces seeking ‘independence.’”

China’s official Xinhua News said the army planned to conduct live-fire drills from Aug. 4 to Aug. 7 across multiple locations. An image released by the news agency indicated that the drills were to take place in six different areas in the waters surrounding Taiwan.

Chinese Foreign Minister Wang Yi said Washington's betrayal “on the Taiwan issue is bankrupting its national credibility."

“Some American politicians are playing with fire on the issue of Taiwan," Wang said in a statement that referred to the U.S. as "the world's biggest saboteur of peace."

Back in the United States, 26 Republican lawmakers issued a statement of rare bipartisan support for the Democratic speaker. The statement called trips by members of Congress to Taiwan routine.

Senate Republican Leader Mitch McConnell backed Pelosi’s visit as a display of support for Taiwan’s democracy and said any allegations that her itinerary was provocative were “utterly absurd.”

“I believe she has every right to go,” McConnell said in a Senate speech.

Senators are considering legislation to bolster Taiwan’s defense as direct response to China’s rhetoric. The Taiwan Policy Act, which has support from both parties, will be discussed Wednesday by the Senate Foreign Relations Committee.

The package would bolster Taiwan’s defense capabilities with nearly $4.5 billion in security assistance over the next four years and provide other support for Taiwan’s democratic government and civil society. The measure would also designate Taiwan as a “major non-NATO ally,” which opens the door to more security and trade benefits.

Backers call it the most comprehensive restructuring of U.S. policy toward Taiwan since the Taiwan Relations Act of 1979.

Pelosi's trip was not officially announced ahead of time.

Barricades were erected outside the Grand Hyatt Hotel in Taipei. Journalists and onlookers thronged the streets just outside and pressed against the hotel's lobby windows as they awaited Pelosi's motorcade. Two buildings in the capital lit up LED displays with words of welcome, including the iconic Taipei 101 building, which said “Welcome to Taiwan, Speaker Pelosi.”

China has stepped up overflights and other provocative moves toward Taiwan and neighboring territory in recent years, asserting broad claims of its rights around the region.

China’s military threats have driven concerns about a new crisis in the 100-mile-wide (140-kilometer) Taiwan Strait that could roil global markets and supply chains.

The White House insisted that China had no valid cause for anger.

“The United States will not seek, and does not want, a crisis,” John Kirby, spokesman for the National Security Council, told a White House briefing Tuesday. “At the same time, we will not engage in saber-rattling.”

U.S. officials have said the American military will increase its movements in the Indo-Pacific region during Pelosi's visit. The aircraft carrier USS Ronald Reagan and its strike group were in the Philippine Sea on Monday, according to officials who spoke on condition of anonymity to discuss military operations.

The Reagan, the cruiser USS Antietam and the destroyer USS Higgins left Singapore after a port visit and moved north to their home port in Japan.

Meanwhile, Taiwan's Defense Ministry said early Wednesday that China had sent 21 planes flying toward Taiwan, 18 of them fighter jets. The rest included an early warning plane and an electronic warfare plane.

Beijing sees official American contact with Taiwan as encouragement to make the island’s decades-old de facto independence permanent, a step U.S. leaders say they don’t support. Pelosi, head of one of three branches of the U.S. government, is the highest-ranking elected American official to visit Taiwan since then-Speaker Newt Gingrich in 1997.

Pelosi’s aircraft, an Air Force version of the Boeing 737, took a roundabout route, flying east over Indonesia rather than directly over the South China Sea.

The speaker has long challenged China on human rights, including traveling to Tiananmen Square in 1991, two years after China crushed a wave of democracy protests.

In 2009, she hand-delivered a letter to then-President Hu Jintao calling for the release of political prisoners. She had sought to visit Taiwan’s island democracy earlier this year before testing positive for COVID-19.

China has been steadily ratcheting up diplomatic and military pressure on Taiwan. China cut off all contact with Taiwan’s government in 2016 after President Tsai Ing-wen refused to endorse its claim that the island and mainland together make up a single Chinese nation, with the communist regime in Beijing being the sole legitimate government.

Pelosi kicked off her Asian tour Monday in Singapore. She is to travel to Japan and South Korea later this week.