The first public hearing into Russian interference in the US election will take place on March 20, with top intelligence officials invited to take the stand in Congress on the snowballing controversy.

Devin Nunes, the chair of the House of Representatives intelligence committee which is probing the allegations dogging the government of President Donald Trump, announced the hearing on Tuesday.

Top US intelligence officials including FBI director James Comey, NSA director Mike Rogers, former CIA director John Brennan, former Director of National Intelligence James Clapper, and former acting attorney general Sally Yates have been invited to take part, he said.

“I want to conduct as many of these hearings in open in the public,” said Nunes. 

“That’s a little rare for the intelligence committees to do,” he noted, saying he was taking the step “because of the seriousness of the accusations involved on all sides.”

The panel will examine a wide range of subjects related to Russia’s activities, including contacts by members of Trump’s campaign with Russian officials; alleged leaks by US intelligence officials on the matter to media; and Trump’s accusation Saturday that former president Barack Obama had US intelligence or law enforcement wiretap his Trump Tower in New York.

US intelligence agencies have publicly accused Russian President Vladimir Putin of masterminding the operation to interfere in last year’s election, but there remain huge questions over media reports saying Trump aides and advisors had regular contact with Russian officials during the campaign.

The Senate Intelligence Committee has already held closed-door hearings into the matter, but nothing has been reported from those sessions publicly.

Democrats are meanwhile demanding the Justice Department name an independent prosecutor to investigate, fearing that politics could taint any probes by Congress or the department.

Earlier Tuesday Democrats pressed Trump’s nominee for deputy attorney general, Rod Rosenstein, to confirm that he would back a special independent prosecutor if the facts supported it.

If confirmed in the job Rosenstein would likely be the one to decide, as Attorney General Jeff Sessions had to recuse himself from any Russia-related investigations last week because of his own meetings with Russia’s ambassador to Washington last year.