China has opposed the flag hoisting by Taiwan's de facto embassy in Washington on New Year's Day and urged the U.S. to respect the "One China" policy.
According to Stuff.co.nz, the US State Department said that the flag hoisting was inconsistent with the U.S. policy and that it had not been notified about the ceremony in advance.
China holds that there is only one China and that Taiwan is a part of the country.
It was the first time that the Taiwanese flag was hoisted in the U.S. in 36 years since Washington switched recognition from Taiwan to Beijing in 1979.
There were more than 100 people at the ceremony on Thursday including Taiwan's top envoy.