HANOI (AP) — U.S. Vice President Kamala Harris delivered a sharp rebuke to China for its incursions in the South China Sea, warning its actions there amount to “coercion” and “intimidation” and affirming that the U.S. will support its allies in the region against Beijing’s advances.

“We know that Beijing continues to coerce, to intimidate and to make claims to the vast majority of the South China Sea,” she said in a foreign policy speech Tuesday in Singapore in which she laid out the Biden administration’s vision for the Indo-Pacific. “Beijing’s actions continue to undermine the rules-based order and threaten the sovereignty of nations.”

Harris, who is on a weeklong swing through Southeast Asia, declared that the U.S. “stands with our allies and our partners” in the face of threats from China. Her subsequent stop in Vietnam was delayed several hours due to an investigation into two possible incidents of the so-called Havana syndrome — a mysterious health ailment plaguing U.S. diplomats — in Hanoi.

The speech sought to cement the U.S. commitment to supporting its allies in an area of growing importance to the Biden administration, which has made countering China’s influence globally a centerpiece of its foreign policy. And it came during a critical moment for the United States, as the Biden administration seeks to further solidify its pivot toward Asia while America’s decades-long focus on the Middle East comes to a messy end with the chaotic withdrawal from Afghanistan.

Harris underscored this shift, calling the Indo-Pacific “critically important to our nation's security and prosperity.” She said that while the U.S. is focused on closing out its Afghanistan engagement by evacuating as many people as possible, “it is also imperative that as we address developments in one region, we continue to advance our interests in other regions, including this region.”

Her rebuke to Beijing amounted to her sharpest comments yet on the U.S. foe. And China hit back, with Chinese Foreign Ministry spokesperson Wang Wenbin invoking Afghanistan in his response to a question about Harris’ comments, saying the messy withdrawal from Kabul showed the U.S. had lost credibility. He charged that the U.S. “can smear, suppress, coerce, and bully other countries at will in order to maintain America first, without paying any price.”

"This is the order that the U.S. wants. The U.S. always tries to make use of the rules and order to justify its own selfish, bullying and hegemonic behavior, but who still believe it now?” Wang said.

In her remarks, Harris was careful to emphasize that the U.S. is seeking greater engagement in the Indo-Pacific region not just to counter China, but to advance an “optimistic vision that we have for our participation and partnership in the region." In deference to Singapore's staunch neutrality in the U.S.-China dispute, Harris also affirmed that the U.S. isn't looking to “make anyone choose between countries."

Speaking in a country that serves as the anchor of the U.S. naval presence in Southeast Asia, Harris emphasized the significance the region holds for U.S. defense. She also emphasized the significant U.S. economic ties there, noting that Southeast Asia represents America's fourth largest export market.

After the speech Tuesday, Harris held a roundtable discussion with business leaders on supply chain issues. And after a delay of several hours that her staff refused to explain, Harris departed for Vietnam, the trip's second and final stop. She meets with top Vietnamese officials on Wednesday.

The U.S. Embassy in Hanoi issued a statement saying the delay was because Harris’ office learned about a report of a “recent possible anomalous health incident” in the Vietnamese capital. The embassy provided no details, but said Harris’ office decided to travel to Hanoi “after careful assessment.”

The cause of the delay was two reported, separate cases of the so-called Havana Syndrome, according to an administration official not authorized to speak publicly about an ongoing investigation. The people potentially afflicted were not immediately identified.

The U.S. government uses “anomalous health incident” to describe the syndrome, a rash of mysterious health incidents first reported by American diplomats and other government employees in Havana, Cuba, beginning in 2016. Some of those impacted report hearing a loud piercing sound and feeling intense pressure in the face. Pain, nausea, and dizziness sometimes followed.

Similar, unexplained health ailments have since b een reported by Americans serving in other countries. Administration officials have speculated that Russia may be involved, a suggestion Moscow has denied.

President Joe Biden himself has repeatedly emphasized his focus on China as one of America’s main adversaries. In recent months, his administration has ramped up outreach to the Indo-Pacific region, with Defense Secretary Lloyd Austin and Deputy Secretary of State Wendy Sherman both visiting the area in the spring and summer. Secretary of State Antony Blinken also held a number of virtual meetings with Southeast Asian officials earlier this month.

The chaotic U.S. withdrawal from Afghanistan, however, complicated that message of support to the region, raising questions about the U.S. commitment to its allies. While Biden said last week that an indefinite engagement would have benefited “true strategic competitors” China and Russia, China has seized on the images of violence from the evacuation to slam the U.S. for its engagement there.

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Additional reporting contributed by Associated Press writers Jonathan Lemire in Lowell, Mass. and Matthew Lee and Darlene Superville in Washington.