Special counsel Robert Mueller has asked the White House to turn over all its documents related to Donald Trump Jr.'s initial statement on a meeting with a Russian lawyer at Trump Tower.

The statement, which was reportedly drafted on Air Force One and approved by President Trump, was later shown to be false after Trump Jr. released his email correspondence about setting up the meeting.

Mueller's investigative team has taken a broad approach to the probe, requesting any and all documents related to the controversies that have cast a cloud over the Trump administration - namely the controversial meeting between Trump's eldest son and a Russian lawyer who promised compromising information on Democratic candidate Hillary Clinton ahead of the 2016 election.

Politico reported Thursday that phone records from Air Force One were included in the document request.

The request follows reports that Mueller hoped to interview White House staffers who were present at the time Trump dictated Trump Jr.'s initial statement.

Trump Jr. has become a key figure in the various Russia probes following reports of the meeting. He has repeatedly denied that he received any damaging information about Clinton.

Trump Jr. met with Senate investigators behind closed doors earlier this month.

Mueller's investigation appears to be picking up steam as he continues to look into whether Trump campaign associates colluded with the Russians to sway the election in their favor.