China on Monday warned students and academics on the "risk" of studying in the United States, citing an uptick in visa denials and delays amid a trade war and other tensions.

The ministry said Chinese students and academics have experienced visa restrictions, delays in obtaining them, and visas with shorter duration.

China is the biggest source of international students on US campuses, with 360,000 of them last year, or a third of the foreign student body, with many paying full tuition.

The warning comes after FBI director Christopher Wray said in April that Beijing has used Chinese graduate students and researchers, among others, in its economic espionage efforts in the United States.

Last month, Republicans in the US Congress introduced legislation aimed at barring Chinese military scientists from obtaining visas to study or work in the United States.

The bills in the House and Senate would compel the White House to identify a list of research and scientific institutions that the president determines are affiliated with or funded by the People's Liberation Army.

The PLA Visa Security Act would prevent people currently or formerly employed or sponsored by such entities from entering the United States on student or research visas.

China's state-run Global times has published accounts from several Chinese academics saying their 10-year visas to the US were cancelled, with officials citing concerns about links to Chinese intelligence.

US scholar Michael Pillsbury, who advises US President Donald Trump on China, said his visa to enter the country for a forum earlier this year was blocked in apparent retaliation.

(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)