The FBI said Monday it is investigating how thousands of Democratic National Committee emails were hacked, a breach that Hillary Clinton's campaign maintains was committed by Russia to benefit Donald Trump.

A statement from the FBI confirmed that it is 'investigating a cyber intrusion involving the DNC,' adding that 'a compromise of this nature is something we take very seriously.'

Wikileaks posted emails Friday that suggested the DNC was favoring Clinton over her rival Sen. Bernie Sanders during the primary season, prompting Clinton's campaign to point to a massive hacking of DNC computers in June that cybersecurity firms linked to the Russian government.

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Supporters of Bernie held up their own candidate's signs – as well as signs reminding her of the hacked email scandal, during her appearance Monday

DRAMA: The tumult took place just as the Democrats are kicking off their convention – and hoping to put on a show of unity that would contrast with the emotional clashes that took place at the Republican Convention last week in Cleveland

Clinton campaign chairman John Podesta added fuel to the debate Monday, saying there was 'a kind of bromance going on' between Russian President Vladimir Putin and Trump.

The Clinton campaign says Russia favors Trump's views, especially on NATO.

Donald Trump on Monday dismissed as a 'joke' claims by Hillary Clinton's campaign that Russia is trying to help Trump by leaking thousands of emails from the Democratic National Committee.

'The new joke in town is that Russia leaked the disastrous DNC e-mails, which should have never been written (stupid), because Putin likes me,' Trump wrote as part of a series of Tweets. 'Hillary was involved in the e-mail scandal because she is the only one with judgement (sic) so bad that such a thing could have happened.'

The hacking enraged die-hard Sanders supporters who have long claimed that the DNC had its finger on the scale throughout the primaries.

The disclosures prompted the resignation of DNC chairwoman Debbie Wasserman Schultz on the eve of the party's convention in Philadelphia, where Clinton is expected to officially accept the nomination for president.

It wasn't immediately clear how WikiLeaks received copies of the internal Democratic emails, though a hacker who calls himself 'Guccifer 2.0' has taken credit for passing the DNC's documents along.

Among them, one exchange shows DNC Chief Financial Officer Brad Marshall floating the idea that Sanders religious beliefs, or lack thereof, could boost Clinton's standing in Kentucky and West Virginia.

The revelations in the WikiLeaks hack prompted runner-up Bernie Sanders to call for Wasserman Schultz's resignation on Sunday

Clinton barely squeezed out a win in Kentucky, while got walloped by Sanders in West Virginia.

'Does he believe in a God. He had skated on saying he has a Jewish heritage,' the message said.

'I think I read he is an atheist. This could make several points difference with my peeps. My Southern Baptist peeps would draw a big difference between a Jew and an atheist,' it continued.

Amy Dacey, the committee's CEO, responded in all caps: 'AMEN.

Marshall later apologized.

Other emails exposed in the leak showed the ousted Wasserman Schultz mouthing off.

Writing from a Gmail account that reportedly belonged to the exiting chairwoman she called Sanders' campaign manager Jeff Weaver 'an ASS,' after he suggested that the Vermont senator would stay in the race through the convention.

She also called him a 'damn liar' and accused Weaver of 'scummy behavior' after he made comments she disagreed with about potential protests in Nevada.

Wasserman Schultz also labeled Trump a 'sexist pig,' upon hearing that the Republican made comments about Clinton 'shouting that message.'

Another exchange suggests that the Democratic National Committee encouraged party activists and even interns to attend anti-Donald Trump protests.

Democratic Party officials learned in late April that their systems had been attacked after they discovered malicious software on their computers.

A cybersecurity firm they employed found traces of at least two sophisticated hacking groups on the Democrats' network — both of which have ties to the Russian government.