WASHINGTON (Reuters) - The partisan divide over the House Intelligence Committee’s probe of Russian interference in the U.S. presidential election deepened on Friday, when the committee’s top Democrat suggested its Republican chairman canceled a public hearing after pressure from the White House.

Panel chairman Devin Nunes said he had to cancel next Tuesday’s hearing with officials from former Democratic President Barack Obama’s administration in order to have a classified briefing with the directors of the National Security Agency and Federal Bureau of Investigation.

“The committee seeks additional information ... that can only be addressed in closed session,” Representative Nunes told reporters.

FBI Director James Comey and NSA head Admiral Mike Rogers testified at a public hearing on Monday at which Comey confirmed for the first time that the FBI is investigating possible ties between Republican President Donald Trump’s campaign as Moscow sought to influence the 2016 election.

Representative Adam Schiff, the intelligence committee’s top Democrat, said the cancellation was not in the public interest.

“I think that there must have been a very strong pushback from the White House about the nature of Monday’s hearing. It’s hard for me to come to any other conclusion about why an agreed upon hearing would be suddenly canceled,” Schiff told a separate news conference.

The scheduled witnesses, former Director of National Intelligence James Clapper, former Central Intelligence Agency Director John Brennan and former Deputy Attorney General Sally Yates, were in office when the purported hacking and disinformation by Russia to influence the election took place.

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Russia has denied allegations by U.S. intelligence agencies that it sought to influence the election, and Trump, a Republican, has said the controversy was cooked up by Democrats and fanned by hostile media.

CAMPAIGN AND CREDIBILITY

Nunes also said on Friday that former Trump campaign manager Paul Manafort’s lawyers told the committee that he is volunteering to be interviewed, and that the panel would work with his lawyers to decide whether the interview would be open or closed to the public.

The New York Times reported last month Manafort was one of several Trump advisers whose contacts with Russian operatives were monitored by U.S. law enforcement and intelligence.

Manafort, who was Trump’s campaign chairman for several months last year, dismissed the report, the newspaper said.

Many Democrats, including Schiff, have questioned whether a committee led by Nunes, a close Trump ally who served on the president’s transition team, can still be relied on to conduct a credible investigation.

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They have called for a special prosecutor or select committee.

Nunes apologized to the intelligence panel on Thursday for announcing to the public and briefing Trump that U.S. intelligence may have swept up communications by Trump associates before telling the committee.

Schiff said Democrats had no intention of giving up on the investigation.

“From my point of view, that would be irresponsible of us. So, I think we’re going to do our best to investigate this regardless of the obstacles we’re encountering,” Schiff said.

Trump, who in early March tweeted without giving evidence that Obama had wiretapped his campaign while the businessman competed against Democrat Hillary Clinton, said he was “somewhat vindicated” by Nunes’ statement about the surveillance.