During a meeting with Vietnamese President Nguyen Xuan Phuc, Harris expressed Washington’s desire to elevate its relationship with Hanoi from a comprehensive to a strategic partnership, a title that could entail deeper security cooperation.

Vietnam is among half a dozen South China Sea littoral states that claim features in the energy-rich waters, where a number of important sea lanes facilitate about one-third of global trade by sea. It is around the China-controlled Paracel Islands—known as Xisha in Chinese—where Hanoi and Beijing have clashed most notably in the past.

“We need to find ways to pressure and raise the pressure, frankly, on Beijing to abide by the United Nations Convention on the Law of the Sea, and to challenge its bullying and excessive maritime claims,” Harris told Nguyen.

The remarks echoed her similar rebuke of China while speaking in Singapore on Tuesday, when she accused China of coercion and intimidation in the sea.

Among its allies and partners in the region, the U.S. remains the only country to have regularly conducted freedom of navigation operations in the waters around the Paracel Islands, irking China on each occasion.

Harris committed to maintaining the U.S.’ “strong presence in the South China Sea” to counter Beijing’s sweeping claims to almost the entire area.

Harris’ visit makes her the first vice president to visit Vietnam. She told President Nguyen that the U.S. would strengthen the bilateral relationship and support a “strong, prosperous and independent Vietnam.”

“Our relationship has come a long way in a quarter of a century,” she said.

In a bilateral meeting with Vietnamese Prime Minister Pham Minh Chinh, Harris announced a donation of 1 million Pfizer vaccines to the country, where only a small percentage of the population is vaccinated amid a surge of the Delta variant. The additional doses, to arrive within 24 hours, brings the total donation to Vietnam to 6 million.

The vice president also was to attend an additional health security meeting on Wednesday, as well as speak ahead of the opening of a Southeast Asia regional office for the Centers for Disease Control and Prevention.

Harris’ weeklong swing through Singapore and Vietnam unsurprisingly has been overshadowed by the ongoing withdrawal of U.S. personnel from Afghanistan. Her delegation in Southeast Asia is seen as the U.S.’ attempt to reinforce its commitments to the Indo-Pacific region.

Acutely aware of Washington’s moves to bolster ties with some of its neighbors, China arranged a meeting between its top envoy in Hanoi and the prime minister of Vietnam on Tuesday, before Harris arrived in the country.

In his meeting with Chinese Ambassador Xiong Bo, Prime Minister Pham emphasized Vietnam’s pursuit of an independent foreign policy that would not involve choosing sides, according to a report by the Vietnam News Agency.

“Vietnam does not ally with one country to fight the other,” he told the Chinese diplomat.