As US-China relations reach a boiling point, Washington has started to screen Chinese students at airports for technology theft.

When Boston Logan International Airport’s announcement asked Keith Zhang to come to the boarding desk, he thought it was a regular boarding check.

But when he saw two armed American officers expecting him there, his heart sank.

“They questioned me under the premise that I am here to steal technology,” Keith Zhang – not his real name – tells the BBC.

Zhang, a 26-year-old PhD student from China, was a visiting researcher at Brown University’s department of psychological sciences for a year.

He had not expected to spend his last two hours on US soil being interrogated about his potential ties with the Chinese Communist Party.

So what might have happened?

FBI director Christopher Wray recently said, in response to Beijing’s “far-reaching campaign” of economic espionage, the FBI is now opening a new China-related counterintelligence case every 10 hours.

In July, Washington closed the Chinese consulate in Houston, calling it a “spy centre”.

As the US tightens its scrutiny of Chinese nationals over espionage concerns, screening selected departing Chinese students and researchers appears to be Washington’s new measure to counter economic espionage. Some of the students’ electronic devices were taken away for further examination and not returned for weeks.

Zhang describes the screening as “pure harassment”.

“If I were to steal any data or intellectual property, I could send it through cloud storage. Taking away my laptop and phone for examination does nothing more than harassment,” Zhang says.

China’s foreign ministry accuses Washington of “abusing” the judicial power to interrogate and arrest Chinese students in the US “under fabricated allegations”.

However, a series of indictments against Chinese researchers suggest the suspicions of US authorities have some grounds.

In August, Haizhou Hu, a 34-year-old Chinese visiting scholar at the University of Virginia, was arrested when he attempted to board a flight to China at Chicago O’Hare International Airport.

The Department of Justice said “a routine screening” revealed that his laptop contained research-related software code, which he was not authorised to possess. The code has military applications, according to a federal indictment.