A computer network cable is seen above a Chinese flag in this July 12, 2017 illustration photo.
A computer network cable is seen above a Chinese flag in this July 12, 2017 illustration photo. Reuters / THOMAS WHITE

U.S. companies are hosting customer data more often on servers in China, complicating U.S. authorities' ability to get information for criminal investigations, a senior federal prosecutor said on Wednesday.

Carolyn Pokorny, the top deputy U.S. Attorney in Brooklyn, said at a cybersecurity conference at New York's Fordham University that U.S. service providers have told prosecutors they cannot respond to some search warrants because the data being sought is held by a China-based entity.

"By moving the data to the PRC, service providers are increasingly putting evidence of crimes out of the reach of prosecutors and agents," Pokorny said, referring to the People's Republic of China.

U.S. prosecutors frequently serve court-approved search warrants on internet and telephone service providers, to seek evidence of crimes within suspects' electronic communications.

Pokorny declined to provide details on specific cases in which prosecutors could not access data stored in China.

Liu Pengyu, a spokesman for China's embassy in Washington, said in a statement that the United States could seek China's help in criminal justice matters under a mutual legal assistance treaty the two countries signed in 2001.

Pokorny said the problem stems from Beijing's efforts to get companies to store Chinese customers' data in China, rather than the United States and Europe.

That could result in U.S. residents ending up with data stored in China, she said.

Beijing can also use its control over electronic data to target dissidents living abroad, Pokorny said.

U.S. prosecutors have accused several individuals of intimidating U.S.-based critics of China on behalf of the government in Beijing.

Speaking at the same conference, Damian Williams, the top federal prosecutor in Manhattan, encouraged service providers that learn of criminal activity through data they host to report it to law enforcement rather than wait for search warrants.