The U.S. has had troops in Taiwan training local forces to better defend themselves in case of attack by China, according to a U.S. defense official, an acknowledgment that could challenge Washington’s recent thaw with Beijing.

The official, who asked not to be identified, confirmed an earlier report by The Wall Street Journal that more than two dozen American service members, including special forces, have been in Taiwan for more than a year. Some of the training has been with local maritime forces on small-boat exercises, according to the Journal.

The Pentagon, which historically has not disclosed details about U.S. training or advising of Taiwanese forces, did not specifically comment on or confirm the deployment.