Yunqing Jian, 33, and Zunyong Liu, 34, are charged with conspiracy, smuggling, false statements, and visa fraud, the US Attorney's Office for the Eastern District of Michigan said in a statement.

Jian is in US custody while Liu's whereabouts are unknown.

The Justice Department said the pair conspired to smuggle a fungus called Fusarium graminearum into the United States that causes "head blight," a disease of wheat, barley, maize, and rice.

The fungus is classified in scientific literature as a "potential agroterrorism weapon," it said, and causes billions of dollars in losses each year.

It causes vomiting, liver damage, and reproductive defects in humans and livestock, it said.

According to the complaint, Jian and Liu, her boyfriend, had both previously conducted work on the fungus in China.

"(Liu) first lied but then admitted to smuggling Fusarium graminearum into America... so that he could conduct research on it at the laboratory at the University of Michigan where his girlfriend, Jian, worked," the Justice Department said.

US Attorney Jerome Gorgon Jr described the smuggling of the fungus into the United States as a "national security" concern and emphasized Jian's membership in the Chinese Communist Party.

"These two aliens have been charged with smuggling a fungus that has been described as a 'potential agroterrorism weapon' into the heartland of America, where they apparently intended to use a University of Michigan laboratory to further their scheme," Gorgon said.

Chinese foreign ministry spokesman Lin Jian said he was not aware of the case when asked for comment at a regular news briefing on Wednesday.

"The Chinese government has always required Chinese citizens overseas to strictly abide by local laws and regulations, and at the same time safeguards the legitimate rights and interests of Chinese citizens overseas in accordance with the law," he said.

US Secretary of State Marco Rubio vowed last week to "aggressively revoke visas" for Chinese students, a move condemned by Beijing as "unreasonable" and "discriminatory."

Kseniia Petrova, a scientist from Russia at Harvard, is facing potential deportation after she failed to declare biological samples in her luggage upon returning from a trip to Paris.