The FBI acquired and tested a hacking tool made by Israeli surveillance company NSO Group but said it did not use the tool in an investigation.
NSO, which makes the Pegasus software, has been criticised after it was revealed its surveillance tools were misused by governments and other agencies to hack iPhones.
The company has said its technology is intended to help to catch terrorists, paedophiles and hardened criminals. NSO is being sued by Apple for breaching its user terms and services agreement.
It did not immediately respond to a request for comment from Reuters.
"The FBI procured a limited licence for product testing and evaluation only; there was no operational use in support of any investigation," an FBI representative said on Wednesday, confirming reports in The New York Times and The Guardian newspaper.
The US law enforcement agency said its licence was no longer active.
NSO, which has long kept its client list confidential, has said that it sells its products only to "vetted and legitimate" government clients. Security researchers and academics have found that NSO's tool has been used against political dissidents, journalists and activists.
The FBI's admission comes after the US National Counterintelligence and Security Centre posted on Twitter last month that software being peddled by surveillance companies was "being used in ways that pose a serious counterintelligence and security risk to US personnel and systems."
Late in 2021, the US Commerce Department added NSO to a blacklist over human rights concerns.
In 2020, Reuters reported that the FBI was investigating the role of NSO in possible hacks on American residents and companies.
The FBI did not immediately return a message seeking comment on the status of the inquiry, which Reuters said had been under way since at least 2017.
