US President Donald Trump's son-in-law, Jared Kushner, will cooperate with the Federal Bureau of Investigation (FBI) as it looks into his ties with Russia, according to a statement from Kushner's attorney released on Friday.

"Mr. Kushner previously volunteered to share with Congress what he knows about these meetings. He will do the same if he is contacted in connection with any other inquiry," the statement from attorney Jamie Gorelick said.

The statement came the same day the House oversight committee asked the FBI to hand over more documents - some dating back nearly four years - concerning ex-FBI head James Comey's interactions with the White House and the Justice Department. The oversight committee is also looking into Russian meddling in the 2016 presidential election.

Kushner a key figure in Trump administration

Meetings between Kushner and Russian officials in December have come under scrutiny as part of an investigation into potential Russian meddling in the US election, The Washington Post newspaper and the broadcaster NBC reported. 

Kushner, a key White House adviser who is married to Trump's daughter Ivanka, reportedly met late last year with Russian ambassador Sergey Kislyak and Russian banker Sergey Gorkov.

The Washington Post cited anonymous "people familiar with the investigation," who said the FBI investigation did not mean Kushner was suspected of a crime.

Gorkov is chairman of VneshEconomBank, a state bank under US sanctions since July 2014.

Kushner initially failed to declare the meetings in forms required to obtain security clearance to serve in the White House. His lawyer later said it was a mistake, telling the FBI that he would amend the forms.

Kushner is the only current White House official named as a key figure in the FBI probe, which is targeting other members of Trump's campaign team.

Kushner and Kislyak discussed back channel

Several current and former US officials told Reuters that Kushner had at least three previously undisclosed contacts with Kislyak. Kushner said that he does not recall any contact with Kislyak.

But Kushner suggested setting up a back channel between Trump's transition team and Russia in December, according to The Washington Post. The newspaper report says Kislyak told his superiors that Kushner suggested a communications channel between Trump and Russia in December. Trump's first national security adviser was also with Kislyak and Kushner when they discussed the communication channel. The FBI considers the meeting worthy of investigating.

Trump campaign committee to be investigated

The Senate Intelligence Committee has asked Trump's political organization to hand over all documents going back to the campaign's launch in 2015, according to The Washington Post. The request includes emails and telephone records. This is the first time the campaign committee has been pulled into the FBI probe.

The letter was signed by Republican Senator Richard Burr, the committee chairman, and Democratic Senator Mark Warner. Both senators declined to comment on the letter, according to the Post.

The Trump campaign committee is based at the Trump Tower in New York City and is currently headed by former deputy campaign manager Michael Glassner and John Pence, a nephew of Vice President Mike Pence.

Joe Lieberman out of leadership run

Joe Lieberman, a former US Senator and vice presidential candidate, withdrew from consideration as the next director of the FBI on Thursday due to a potential conflict of interest.

Lieberman currently works at a New York City law firm led by Marc Kasowitz, whom Trump hired to represent him against collusion investigations by the Justice Department and Congress, which are being conducted concurrently with that of the FBI. The law firm, Kasowitz Benson Torres LLP, has represented Trump on many occasions over previous years.

"With your selection of Marc Kasowitz to represent you in the various investigations that have begun, I do believe it would be best to avoid any appearance of a conflict of interest," Lieberman wrote in a letter to Trump on Wednesday, which was made public on Thursday.

Lieberman was considered a top candidate to become FBI director. Trump said last Thursday that he was "very close" to selecting a new director. The White House did not release an immediate comment on Lieberman's withdrawal.

Trump fired the previous FBI director, James Comey, on May 9. In his role, Comey led the FBI's campaign collusion probe. Trump and Russia have both denied the accusations.

Lieberman served as a Senator from Connecticut from 1989 until he retired in 2013. He was the Democratic vice presidential candidate during the 2000 US presidential election, but later left the Democratic party to serve as an independent.

aw, kbd/kl (AFP, AP, Reuters, dpa)