Washington, Sep 30 (IANS): Special counsel Robert Mueller has started interviewing White House officials as part of the investigation into alleged Russian meddling in the 2016 presidential election, a media report said.

Informed sources told Fox News on Friday that retired Lt. Gen. Keith Kellogg, the chief of staff for the National Security Council, was interviewed on Thursday.

The questioning covered former national security adviser Michael Flynn, who resigned in February and who helped bring Kellogg onto President Donald Trump's transition team.

The sources said Kellogg was shown records related to the investigation of Flynn.

Mueller's team was expected to start interviewing White House staffers, having already sought a wide variety of documents related to their Russia probe.

In a separate development, Fox News has learned that congressional investigators as well as federal agents are scrutinising a Trump campaign national security meeting in March 2016 at Washington, D.C.'s Old Post Office, now the site of the Trump International Hotel.

During the meeting, a staffer named George Papadopoulos reportedly suggested setting up a meeting with senior Russian officials about repairing the washington-Moscow relationship.

The sources told Fox News that then-senator Jeff Sessions shut down the discussion, with others following up via email that such a meeting might violate the Logan Act -- a 200-year-old statute that bars American citizens from engaging with a foreign government without authorisation from the incumbent government.