Washington (CNN) Justice Department Special Counsel Robert Mueller has issued grand jury subpoenas related to Donald Trump Jr.'s 2016 meeting with a Russian lawyer at Trump Tower, according to a person familiar with the matter.

The subpoena seeks both documents and testimony from people involved in the meeting, CNN has learned. That meeting has drawn scrutiny since an email exchange beforehand indicated the Russians offered damaging information on Hillary Clinton.

The moves signal a new step in the investigation, which Trump has lambasted as a "witch hunt." Trump has denied any collusion between his team and the Russians. US intelligence agencies have concluded that Russia attempted to sway the presidential contest in Trump's favor.

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