(CNN) Jared Kushner has turned over documents in recent weeks to special counsel Robert Mueller as investigators have begun asking in witness interviews about Kushner's role in the firing of FBI Director James Comey, CNN has learned.

Mueller's investigators have expressed interest in Kushner, President Donald Trump's son-in-law and a White House senior adviser, as part of its probe into Russian meddling, including potential obstruction of justice in Comey's firing, sources familiar with the matter said.

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. It is not clear how Kushner's advice to the President might relate to the overall Russia investigation or potential obstruction of justice.

Sources close to the White House say that based on their knowledge, Kushner is not a target of the investigation.

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

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