The State Department’s request to the Pentagon for a Marine detachment to help secure an unofficial American embassy in Taiwan has been rejected by Secretary of Defense James Mattis, according to CNN.

Last month, a request by the State Department to send a Marine detachment to a new American Institute in Taiwan was denied by Mattis, according reporting by CNN. A unnamed defense official has told CNN that the Marines were assumed to be arriving in Taiwan in October.

The new American facility, located just outside of the capital of Taipei, will be able to house 450 people, according to the AIT website.

State Department officials did not comment to CNN on the specifics regarding the decision.

This denial ultimately comes at time when affairs between the U.S. and China are rocky.

The U.S. government does not officially recognize Taiwan as a country. This is due to the “One China Policy,” dating back to the early 1970s. China maintains ceremonial rule over Taiwan. However, the U.S. has had an established “de facto American embassy,” since 1979.

The security requirement for AIT will likely be augmented like other de facto embassies or similar unofficial U.S. diplomatic outposts. This is a similar situation to the use of private contractors in the Middle East and Africa, according to CNN.

According to a State Department website, the agency does not does take any type of responsibility for the personnel employed by a list of several security companies that are used by the Department of State for security purposes.