WASHINGTON — Chinese hackers targeted cellphones used by Republican presidential nominee Donald Trump and his running mate, J.D. Vance, two people familiar with the matter said Friday.

It was not immediately clear what data if any may have been taken, but U.S. officials are investigating, according to the people, who were not authorized to publicly discuss an ongoing investigation and spoke on the condition of anonymity to The Associated Press.

An FBI statement did not confirm that Trump and Vance were among the potential targets but said it was investigating “unauthorized access to commercial telecommunications infrastructure by actors affiliated with the People’s Republic of China.”

“Agencies across the U.S. Government are collaborating to aggressively mitigate this threat and are coordinating with our industry partners to strengthen cyber defenses across the commercial communications sector,” the FBI said.

U.S. officials believe Trump and Vance are among several people whose phone numbers are believed to have been targeted and suspect it to be part of a larger cyber-espionage campaign launched by China, the person said.

The New York Times first reported that Trump and Pence had been targeted and said the campaign was alerted by U.S. officials this week.

Trump campaign spokesman Steven Cheung did not offer any details about the Chinese operation but issued a statement accusing the campaign of Democrat Kamala Harris of having emboldened foreign adversaries, including China and Iran.

The FBI has repeatedly warned over the last year about Chinese hacking operations, with FBI Director Chris Wray telling Congress in January that investigators had disrupted a state-sponsored group known as Volt Typhoon. That operation targeted U.S.-based small office and home routers owned by private citizens and companies. Their ultimate targets included water treatment plants, the electrical grid and transportation systems across the U.S.

Last month, Wray said that the FBI had interrupted a separate Chinese government campaign that targeted universities, government agencies and other organizations and that installed malicious software on more than 200,000 consumer devices, including cameras, video recorders and home and office routers.

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Michelle L. Price in New York contributed to this report.