The FBI is "concerned" over reports that secret "police stations" linked to China have been set up across the US and Canada, a report said.
A September report issued by the NGO Safeguard Defenders revealed that Chinese public security bureaus established the "overseas police service stations" in several continents, including two in London and one in Glasgow, the BBC reported.
In North America, it found stations in Toronto and in New York. FBI Drector Christopher Wray, told senior politicians that the agency was monitoring reports of such centres across the country.
"We are aware of the existence of these stations. To me, it is outrageous to think that the Chinese police would attempt to set up shop, you know, in New York, let's say, without proper coordination.
"It violates sovereignty and circumvents standard judicial and law enforcement cooperation processes," he was quoted as saying
Violation of US law
Asked if the stations violated US law, Wray said the FBI was "looking into the legal parameters", reports the BBC.
The senior intelligence official was speaking at a US Senate Homeland Security and Governmental Affairs Committee hearing, where he was grilled by senior lawmakers.
According to the NGO, the units were reportedly created to tackle transnational crime and to provide administrative services to Chinese nationals abroad, such as renewing drivers' licences abroad and other consular services.
However, Safeguard Defenders said they also serve a "more sinister goal", by contributing to "cracking down on all kinds of illegal and criminal activities involving overseas Chinese".
China has however, denied running the overseas stations, the BBC reported.
Wray further said the US had opened a number of charges related to the Chinese government harassing, stalking, monitoring and blackmailing people in the US who had been critical of Chinese President Xi Jinping.
"It's a real problem and something that we're talking with our foreign partners about, as well, because we're not the only country where this has occurred," he added.
(With inputs from IANS)