The FBI is investigating an FBI agent who allegedly leaked classified information to a colleague in an apparent attempt to get the other person fired, according to multiple law enforcement officials and sources familiar with the matter.

The officials spoke on condition of anonymity because they weren’t authorized to discuss the ongoing probe.

The disclosure came to light Friday night, shortly after it was revealed that a U.S. citizen and former military intelligence analyst had written a letter to the FBI requesting a public meeting about the ongoing investigation of the former colleague, who has been a top target of special counsel Robert Mueller’s probe.

The officials said the letter also cited a recent FBI memo, which was reviewed by law enforcement, that suggested the person who wrote the letter had information that could be useful in Mueller’s investigation.

It wasn’t clear why the FBI was investigating the former FBI employee, who worked for the bureau’s Counterterrorism Center in Quantico, Virginia.

Officials declined to say whether the employee was a current FBI employee.

A U.C.L.A. law enforcement official said the employee is cooperating with investigators and has not been charged with any crime.

Officials familiar with Mueller’s ongoing probe declined to comment.

Mueller has not publicly commented on the case.

Mueller’s office has been investigating allegations that the former U.F.C.-trained operative, identified by his initials in letters he sent to the media as K., had provided classified information about a U .

S. person, including names and locations of sensitive sources and methods, to an FBI informant and a foreign intelligence source in Russia.

He also allegedly offered to provide information about sources and methodologies for U.N. Special Envoy Samantha Power to conduct counter-terrorism operations in Russia, according the letter.

Sources familiar with K.’s investigation said he was the target of an ongoing investigation into his conduct that included a federal investigation by the FBI, the FBI’s criminal investigative division and the U.K.’s Serious Organized Crime Agency, and a separate U.H.I.E.O. investigation.

It is unclear whether Mueller’s office is pursuing any charges.

The FBI declined to confirm the existence of any investigation.

Mueller, who took over the investigation from Mueller after the resignation of Robert Mueller in August, has said that he is not investigating the conduct of any former FBI employees who may have been targeted.

He has also said that the Justice Department’s criminal investigation of K.’, who is also known as James Bond, is complete.

Mueller and the Justice and FBI departments declined to address any specific allegations made in the letter, including any potential obstruction of justice.