The directors of the FBI and NSA are set to break their public silence on potential ties between President Donald Trump and Russia, and on his explosive allegation that he was wiretapped by his predecessor Barack Obama.



Federal Bureau of Investigation (FBI) Director James Comey and Mike Rogers of the National Security Agency (NSA) will speak to Congress on Monday, publicly addressing for the first time two issues that have riveted the American public for weeks and have further divided the country's two major political parties.



They are both set to testify before the House Intelligence Committee at a hearing aimed at probing Russia's interference in the 2016 election campaign.

OPINION: Why is Russia so happy with Trump?

Trump and his entourage's possible ties with Russia under President Vladimir Putin have been the subject of much speculation since before Trump was elected on November 8.

US intelligence agencies in January concluded that hackers working for Russia broke into the email accounts of senior Democrat Party members and released embarrassing messages with the aim of helping Trump defeat Hillary Clinton.

Several congressional panels have launched investigations into Russia's alleged interference, including the House and Senate intelligence committees, which have jurisdiction over the nation's 17 intelligence agencies, as well as the House and Senate judiciary committees.

The FBI is also probing Russian interference in the election.



The question remains whether the FBI has opened a criminal investigation into possible ties between Trump campaign aides and Russian officials.



Monday's hearing promises to be a very public showdown between the FBI and politicians, with the national security world certain to watch whether Comey drops a political bombshell.



A congressional panel so far has found no evidence that Trump's campaign colluded with Russia, its chairman said Sunday.

Moscow has denied involvement in the hacks, and Trump has denounced the tumult over alleged Russian connections as a "total witch hunt".

Straining relations

Monday's hearing was also expected to address a second explosive issue: Trump's unsubstantiated accusations that the Obama administration wiretapped his phone at Trump Tower in New York during the campaign.



Trump tweeted on March 4 that Obama had "tapped" his phone.

Obama and an array of other officials have flatly denied the allegation. Obama's top intelligence official, James Clapper, has publicly called the claims false, and congressional leaders briefed on the matter have said they have seen no indication that the allegations are true.

"I hope that we can put an end to this wild goose chase," California Democratic congressman Adam Schiff, a House intelligence committee member, told NBC television on Sunday.



"What the president said was just patently false. And the wrecking ball it has created has just banged into our British allies and our German allies and it's continuing to grow in terms of damage and he needs to put an end to this," Schiff said.

The White House was forced to retract a charge repeated last week by its spokesman Sean Spicer suggesting that Britain's intelligence services aided the Obama administration in the alleged wiretap. The claim has strained relations with one of America's closest allies.



Still, as recently as Friday, Trump repeated the claim in an aside during a White House press conference with Angela Merkel.



"As far as wiretapping, I guess, by this past administration, at least we have something in common, perhaps," Trump told the German chancellor, referring to a WikiLeaks report in 2015 that the US had monitored calls involving Merkel and her top aides for years.

The issue of wiretapping first surfaced last month, when Trump's national security adviser Michael Flynn was forced to resign after it was revealed that he had misled top officials over his contacts with the Russian ambassador to Washington.

Around the same time, The New York Times reported that US intelligence had intercepted calls showing that members of Trump's campaign had repeated contacts with top Russian intelligence officials in the year preceding the election.

READ MORE: Russia's booming 'Trumpomania'

House Intelligence Committee chairman Devin Nunes has said that the intelligence committee probe focuses in part on who revealed that Flynn had unreported private contacts with the Russians over the sanctions issue.



Adding to the intrigue, Trump's attorney general Jeff Sessions recused himself from any Russia-related inquiries after it was learned that he had met twice with the Russian ambassador in the months before Trump took office, and had failed to disclose this during his confirmation hearing when asked a question about such contacts and speaking under oath.

Domestically, the controversy over the wiretapping claim has pulled attention away from Trump's effort to push through other key items on his agenda, including the planned repeal of Obama's healthcare law, tax reform and his controversial travel ban.