Chinese Foreign Ministry spokeswoman Hua Chunying slammed the U.S. on Wednesday after a top Chinese space program official was unable to obtain a U.S. visa to participate in the International Astronautical Congress (IAC) event in Washington, D.C.

Hua has alleged that the U.S. has "weaponized" the issuance of visas for Chinese citizens.

The head of the Chinese delegation to the IAC attempted to get a U.S. visa after an interview on Oct. 12 but was unable to do so. Hua has said that by continuing to not issue visas, the U.S. has "repeatedly defied international responsibilities and obligations and impeded normal international exchanges and cooperation."

Hua also added that “for some time, the U.S. has frequently rejected and delayed visa applications, revoked long-term visas of Chinese applicants and investigated and harassed Chinese scholars, students, business people and scientific and technical personnel.”

The U.S. has cracked down on visas to Chinese nationals under the Trump administration and has even attempted to monitor the activities of Chinese diplomats on American soil. The State Department last week said that Chinese diplomats in the U.S. need to report all meetings they have with local and state officials, as well as educational and state institutions.

Heightened U.S.-China tensions have also resulted in Beijing warning Chinese citizens that they should reassess their prospects of obtaining a U.S. study visa. Chinese undergraduate and graduate students are the largest group of foreign students at American universities.

The U.S. has also denied visas for Chinese scholars due to suspicions of espionage or pushing Chinese propaganda. Trump has cracked down on public funding for American universities if they have a Confucius Institute on their campus. Confucius Institutes are Chinese cultural centers, which have been accused of spreading pro-Beijing propaganda.

Beijing is also proposing changes that would make it harder for Americans with anti-China links to obtain Chinese visas. The changes would target U.S. nationals with ties to the military, the CIA or with human rights groups, among others.