BBC
China sees self-governed Taiwan as a breakaway province that will eventually be part of the country, and has not ruled out the use of force to achieve this.
But many Taiwanese consider themselves to be part of a separate nation, although most are in favour of maintaining the status quo where Taiwan neither declares independence from China nor unites with it.
As well as dropping the phrase, the factsheet, which was updated last Thursday, also says the US will support Taiwan's membership in international organisations "where applicable".
Commenting on the changes, a spokesperson at the American Institute in Taiwan - the US' de facto embassy on the island - told local media that the fact sheet had been "updated to inform the general public about [the US'] unofficial relationship with Taiwan".
"We have long stated that we oppose any unilateral changes to the status quo from either side."
On Sunday, Taiwan's Foreign Minister Lin Chia-lung thanked the US for what he called "positive, Taiwan-friendly wordings".
But in their regular press conference on Monday, Beijing's foreign ministry slammed the move, calling the revision a "serious regression" in the US' stance on Taiwan.
"This sends a wrong and serious signal to separatist forces advocating for Taiwan independence and is another example of the U.S. stubbornly persisting with its wrong policy of using Taiwan to contain China," said Chinese spokesperson Guo Jiakun.
Beijing demands the US "correct its mistakes" after it altered its factsheet on the self-ruled island.
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"We urge the US to immediately correct its mistakes [and] earnestly adhere to the One China principle."