The United States will donate 750,000 doses of COVID-19 vaccines to Taiwan, said Sen. Tammy Duckworth, one of three U.S. senators who made a brief visit to the island Sunday morning as it battles its worst coronavirus outbreak of the pandemic.

Duckworth, D-Ill., arrived in Taiwan with Sens. Chris Coons, D-Del., and Dan Sullivan, R-Alaska, as part of a larger trip to the region. Although the United States has no formal diplomatic relations with Taiwan, a self-governing democracy, it is the island’s most important ally and its main weapons provider. The senators’ visit is likely to go over poorly with China, which claims Taiwan as its territory.

Duckworth said the vaccine donation was part of a plan the White House announced last week to distribute 25 million doses this month across a “wide range of countries” struggling to control the coronavirus.

“We are here today to underscore the bipartisan support for Taiwan and the strength of our partnership,” she said at a news conference at Songshan Airport in central Taipei, where the senators arrived from South Korea.

“I’m here to tell you that the United States will not let you stand alone,” she added.

The senators did not specify which vaccines Taiwan would receive or when they would arrive.

President Tsai Ing-wen, who appeared with the senators, described the vaccines as “timely rain for Taiwan.”

“Your help will be etched on our hearts,” said Tsai, who thanked the Biden administration for including Taiwan among the first places to receive vaccine donations. She also said she hoped that the U.S.-Taiwan partnership would continue to improve. During the three-hour visit, the senators were to discuss security and other issues with Tsai and other senior Taiwanese leaders.

After shielding itself from the coronavirus for more than a year, Taiwan has recorded several hundred new infections a day for the past three weeks. On Sunday, health officials reported 343 new local infections, including eight from last week, and 36 deaths. Although such numbers are low by international standards, the outbreak has strained Taiwan’s health system.

It has also given greater urgency to the island’s vaccination campaign, which has barely begun. Only 3% of Taiwan’s 23.5 million residents have received a first dose, according to a New York Times database, and the government has come under growing criticism over its vaccine procurement. Taiwan has declined offers of vaccines from China, citing safety concerns, and accused China of interfering in its vaccine deals, which Beijing denies.

On Friday, a day after the White House announcement, Taiwan received a donation of 1.2 million doses of the AstraZeneca vaccine from the government of Japan, more than doubling the total number of shots the island has received. Social media in Taiwan has been filled with expressions of gratitude to both Japan and the United States, and Friday evening the Taipei 101 skyscraper displayed messages in Chinese and Japanese, including “Taiwan loves Japan.”