WASHINGTON — President Joe Biden said on Tuesday that he made clear to China’s Xi Jinping that his administration stands firmly behind the United States' longstanding “One China” policy but he also noted that the self-ruled island of Taiwan ultimately makes its own decisions.

Biden made clear he was not encouraging Taiwan's "independence" after using the word an hour earlier to describe the progress he made during a discussion of the island with his Chinese counterpart Monday evening.

"I said that they have to decide — Taiwan, not us. We are not encouraging independence," Biden said on an airport tarmac in New Hampshire, where he was promoting his recently signed infrastructure law.

"We're encouraging that they do exactly what the Taiwan Act requires," he went on, referring to the 1979 law dictating the American approach to the island. "That's what we're doing. Let them make up their mind. Period."

White House officials said the two leaders spoke extensively about Taiwan during their more than three-hour virtual meeting one day earlier.

Tensions have heightened as China has dispatched a growing number of fighter jets toward the island, while the US and its allies sail warships though the Taiwan Strait.

But Biden on Tuesday sought to underscore his support for the Taiwan Relations Act.

“We made very clear we support the Taiwan Act and that’s it,” Biden told reporters while traveling in New Hampshire. “It’s independent. It makes its own decisions.”

US officials downplayed the significance of the statement, noting it was longstanding official US policy. Instead, they said Biden made clear to Xi the US opposes any change to the status quo, or any actions that "undermine peace and stability across the Taiwan Strait."

The Chinese offered a more combative interpretation of the conversation. They said Xi told Biden his country would be compelled to take "resolute measures" if separatist forces in Taiwan cross a "red line," according to a readout from China's Ministry of Foreign Affairs.

"Such moves are extremely dangerous, just like playing with fire. Whoever plays with fire will get burnt," the readout said.

Earlier Tuesday, White House national security adviser Jake Sullivan said Biden reminded Xi during their virtual meeting that he voted as a senator for the Taiwan Relations Act.

“So he understands deeply, firsthand, that the act makes clear that any effort to shape Taiwan’s future by other than peaceful means is of grave concern to the United States,” said Sullivan, speaking at a webinar hosted by the Brookings Institution, a Washington think tank.

The Biden-Xi video conference took place Tuesday morning in Beijing and Monday evening in Washington.

Sullivan said the two leaders also agreed to explore talks on arms control.

In the wake of the summit, US and Chinese officials plan to intensify their engagement on Taiwan, according to Sullivan, who said the two leaders spent a "good amount of time" on the issue. — Agencies