The FBI has contacted lawyers for the whistleblower whose complaint about President Donald Trump's July call with Ukraine's president helped kick-start the House impeachment inquiry.

Initial contacts between the FBI and counsel for the whistleblower took place in October and have continued this month, according to a person familiar with the situation. The investigators indicated they were in the early stages of a probe and no interviews are currently scheduled, according to the person.

The person said the Federal Bureau of Investigation was making no demands for testimony or material, but merely asking for cooperation regarding the focus of the complaint made to the intelligence community's inspector general. The whistleblower's report revealed details of Trump's July 25 call with Ukraine President Volodymyr Zelenskiy.

Trump and his allies have repeatedly demanded that they be told the identity of the whistleblower and be able to confront him or her. But the substance of the complaint has been confirmed by a wide range of witnesses testifying to the impeachment inquiry, as well as the White House's rough transcript of the phone call. The president has said his call with Zelenskiy was "perfect."

The person said it was unclear whether the FBI is conducting a criminal investigation into the details revealed in whistle-blower's complaint.

Other media outlets, including NBC News and Yahoo News, earlier reported the FBI's contacts with the lawyers.