Donald Trump's former national security adviser Michael Flynn has invoked his Fifth Amendment right against self-incrimination in rebuffing a subpoena in the investigation into Russia's election meddling.
A senior House of Representatives Democrat later cited new evidence he said appeared to show Mr Flynn lied on a security clearance background check.
With the president in the Middle East on his first foreign trip as president, investigations into Russian interference in the 2016 campaign – and allegations of Trump campaign collaboration – showed no sign of slackening in Washington.
Mr Flynn's lawyers claimed an "escalating public frenzy" against the former aide justified declining the subpoena for his records.
They told the Senate intelligence committee Mr Flynn will not turn over personal documents sought under the congressional subpoena or otherwise comply as part of its investigation.
Hours later, Elijah Cummings, senior Democrat on the House oversight committee, cited what he said were inconsistencies in Mr Flynn's disclosures to US investigators in early 2016 during his security clearance review.
Mr Cummings said Mr Flynn appeared to have lied about the source of a $33,000 (£25,000) payment from Russia's state-sponsored television network, failed to identify foreign officials he met – including President Vladimir Putin – and glossed over his firing as chief of the Defence Intelligence Agency during the Obama administration.
Mr Cummings made his points in a letter asking the committee's chairman, Jason Chaffetz, to subpoena the White House for documents related to Mr Flynn.
Mr Flynn's lawyers also said earlier in the day that the Justice Department's appointment of a special counsel has created a legally dangerous environment for him to co-operate with the Senate panel's investigation.
Mr Trump appointed the retired US army lieutenant general and top military intelligence chief as his senior national security aide in January, only to fire him less than a month later.
The White House said he had misled top US officials, including vice president Mike Pence, about his contacts with Russian officials, including the ambassador to the US.
Mr Cummings said Mr Flynn repeatedly provided inconsistent or untruthful statements to security clearance investigators in January 2016 before the renewal of his credentials.
