The US is lifting long-standing restrictions on contacts between American and Taiwanese officials, Secretary of State Mike Pompeo says.
The “self-imposed restrictions” were introduced decades ago to “appease” the mainland Chinese government, which lays claim to the island, the US state department said in a statement.
These rules are now “null and void”.
The move is likely to anger China and increase tensions between Washington and Beijing.
It comes as the Trump administration enters its final days ahead of the inauguration of Joe Biden as president on 20 January.
The Biden transition team have said the president-elect is committed to maintaining the previous US policy towards Taiwan.
Analysts say they will be unhappy with such a policy decision being made in the final days of the Trump administration, but that the move could be reversed easily by Mr Pompeo’s successor Antony Blinken.
China regards Taiwan as a breakaway province, but Taiwan’s leaders argue that it is a sovereign state.
Relations between the two are frayed and there is a constant threat of a violent flare up that could drag in the US, an ally of Taiwan.
In a statement on Saturday, Mr Pompeo said the US state department had introduced complicated restrictions limiting the communication between American diplomats and their Taiwanese counterparts.
“Today I am announcing that I am lifting all of these self-imposed restrictions,” he said. “Today’s statement recognises that the US-Taiwan relationship need not, and should not, be shackled by self-imposed restrictions of our permanent bureaucracy.”
He added that Taiwan was a vibrant democracy and a reliable US partner, and that the restrictions were no longer valid.
Following the announcement, Taiwan Foreign Minister Joseph Wu thanked Mr Pompeo, saying he was “grateful”.
“The closer partnership between Taiwan and the US is firmly based on our shared values, common interests and unshakeable belief in freedom and democracy,” he wrote in a tweet.
Last August, US Health and Human Services Secretary Alex Azar became the highest-ranking US politician to hold meetings on the island for decades.
The US also sells arms to Taiwan, though it does not have a formal defence treaty with the country, as it does with Japan, South Korea and the Philippines.
China and Taiwan have had separate governments since the end of the Chinese civil war in 1949.
Beijing has long tried to limit Taiwan’s international activities and both have vied for influence in the Pacific region.
Tensions have increased in recent years and Beijing has not ruled out the use of force to take the island back.
Although Taiwan is officially recognised by only a handful of nations, its democratically-elected government has strong commercial and informal links with many countries.