President Donald Trump's son-in-law, Jared Kushner, is the "very senior" official who directed former National Security Advisor Michael Flynn to contact foreign government officials over a UN resolution condemning Israel, NBC News reported on Friday, citing two sources familiar with the matter.

Flynn pleaded guilty on Friday to lying to the FBI regarding contact he had with then-Russian Ambassador Sergey Kislyak in December 2016. He also admitted to lying about his role in pushing foreign officials to delay or defeat a resolution condemning Israeli settlement building during the presidential transition.

"On or about December 22, 2016, a very senior member of the Presidential Transition team directed FLYNN to contact officials from foreign governments, including Russia, to learn where each government stood on the resolution and to influence those governments to delay the vote or defeat the resolution," according to a court document that Flynn and his attorneys signed.

It is against the law for unauthorized citizens to negotiate with foreign governments. However, the 1799 law that forbids such acts has never been successfully used in a prosecution, and doubts have been raised about whether the law is constitutional.

UN Security Council Resolution 2334 was adopted Dec. 28.

A Friday court filing said that on Dec. 29, 2016, Flynn relayed his conversations with the Russian ambassador to a "senior official" of the transition team at Mar-a-Lago. Flynn told the "senior official" that he and the ambassador had discussed sanctions and their potential impact on the incoming administration's foreign policy goals.

Later Friday, NBC reported, citing two people familiar with the matter, that KT McFarland was the "senior official." She did not respond to NBC's requests for comment.

McFarland was a senior official on the transition team and was later appointed as deputy national security advisor. She left that role in April, but was later nominated as ambassador to Singapore.

Alleged attempts by Flynn and other members of Trump's transition team to stymie the resolution were first reported by Foreign Policy in February.

An attorney for Kushner did not respond to a request for comment from CNBC.