Washington, Nov 3 (IANS): US President Donald Trump's son-in-law Jared Kushner has turned over documents to Special Counsel Robert Mueller as investigators have begun interrogations about the senior advisor's role in the firing of former FBI Director James Comey, the media reported.

Mueller's investigators have expressed interest in Kushner as part of its probe into Russian meddling, including potential obstruction of justice in Comey's firing, informed sources told CNN on Thursday.

Their questions about Kushner signal that Mueller's investigators are reaching the President's inner circle and have extended beyond the 2016 campaign to actions taken at the White House by high-level officials.

However, it was not clear how Kushner's advice to the President might relate to the overall Russia investigation or potential obstruction of justice, the sources said.

Kushner voluntarily turned over documents he had from the campaign and the transition, and these related to any contacts with Russia. The documents are similar to the ones Kushner gave to congressional investigators, they added.

According to the sources, investigators have asked witnesses also about how a statement was issued in the name of Donald Trump Jr. regarding a Trump Tower meeting and about the circumstances surrounding the departures of other White House aides.

A White House official told CNN that the Mueller team's questions about Kushner are not a surprise, and that the senior advisor would be among a list of people who investigators would be asking about.

The disclosures follow this week's indictments Trump's former campaign manager Paul Manafort and his longtime business partner and campaign deputy, Rick Gates.

Both pleaded not guilty.

Former Trump campaign foreign policy adviser George Papadopoulos has pleaded guilty for making a false statement to the FBI about contacts with people connected with the Russian government.