An urgent investigation into whether the Trump administration has compromised the US and UK through its links with Russia has been demanded by a member of the Oversight Committee in the House of Representatives.

Democrat congressman Raja Krishnamoorthi said Michael Flynn's resignation as National Security Adviser following revelations he had discussed sanctions with the Russian ambassador to the US before Donald Trump took office raised major concerns secrets may have been traded with the Kremlin.

"There are several serious significant unanswered questions," Mr Krishnamoorthi told BBC Radio 4's Today programme.

"The biggest is quite simply was General Flynn, in Donald Trump's parlance, one bad hombre who went rogue, or was he directed by someone else to discuss sanctions with the Russian ambassador? What was discussed exactly, and why, and... what do the Russians know about our national secrets? Because at the end of the day we need to protect ourselves and of course our allies like the United Kingdom, and in order to do so we need to understand whether any of our secrets were compromised in the balance."

Republican Jason Chaffetz, who chairs the powerful Oversight Committee, has said his panel won't investigate the circumstances that led to Mr Flynn's resignation, instead deferring to the House Intelligence Committee, which is already probing Russian links with the Trump campaign and administration.

"I think that situation has taken care of itself. I know that the Intel committee is looking into the hacking issue," Mr Chaffetz told reporters on Tuesday.

However, Mr Krishnamoorthi said cross-party momentum was building for greater transparency on all the dealings the Trump team has had with the Kremlin.

"This is not a partisan issue. I'm very heartened that Republican senators such as John McCain, Lindsey Graham and others have also called for a full investigation within the US Senate. We need to do the exact same thing in Congress," he said.

"Half the country at this point has serious questions about the relationship between the Government and the Russian Government. We need to have full and open proceedings in order to answer all the questions that the public has, because this revelation as regards Mr Flynn has added fuel to the fire with regard to all the various conspiracy theories that are out there right now.

"This is unprecedented. I cannot recollect a time recently when a national security advisor lasted all of 25 days, who had discussions with the Russian government, one of our primary adversaries today in the world, with regard to lifting sanctions. Was there a quid pro quo? 'If Russia did X, we will lift sanctions'? What is that 'X'? That's what people are asking.

"We must re-evaluate what the Russians know about our national secrets and how we protect ourselves, and then move on from there."

Meanwhile fellow Democrat congressman Seth Moulton told CNN that if it were confirmed Trump's team had been "conspiring" with the Kremlin, "that's the very definition of treason".

“I mean, let’s not lose perspective on exactly who we’re talking about here,” he said in comments reported by The Hill. "Russia is the number one enemy of the United States of America.”

“If members of the administration are essentially conspiring with Russia – either through the [2016 presidential] campaign earlier or now in the administration itself – I mean, look, Wolf, that’s the very definition of treason,” Mr Moulton told host Wolf Blitzer.