U.S. nuclear-powered attack submarines are operating near North Korean waters to track Pyongyang’s submarine operations, a South Korean media outlet claimed on Friday.

Two U.S. government offices refused to confirm the report, however multiple naval and intelligence experts supported the media’s claim.

“Since last year, the U.S. nuclear-powered submarines have been operating in the international waters near Sinpo – where the North’s submarine base is located at – to conduct the secret tracking operations on North Korean submarines,” Chosun Ilbo reported.

Quoting an anonymous source “who has profound knowledge in the U.S. military,” the media outlet claimed that such operations are