Bernie Sanders lashed out at Hillary Clinton’s allies – and threw in Donald Trump for good measure – during a heated breakfast session with reporters in Des Moines Thursday, countering an array of allegations from the Clinton camp while claiming he’ll win the Iowa caucuses if turnout is large.

The Democratic presidential candidate, who is running almost even with Clinton in most Iowa polls, got animated when he was asked by a Bloomberg Politics journalist about Clinton camp whispers that out-of-state young people may try to show up to caucus.

Sanders reacted with disbelief, and demanded to know the source of the charge. 

“I don't want my integrity and honesty to be impugned,” he said. “This is a lie, an absolute lie. Okay? We will win, or we'll lose -- we do it honestly. I really dislike people suggesting, what? We're going to bring in students from out of state, who are going to perjure themselves by saying they live in Iowa?”

It’s unclear where such a charge originated, though there have been reports about young Sanders supporters organizing online to bring out-of-state volunteers to Iowa – not to caucus, but to knock on doors and help the Sanders cause.

Sanders complained Thursday about the “negative” attacks being leveled against him, and pushed back on Clinton camp claims that his own campaign has turned negative.

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“Donald Trump is a pathological liar!” he exclaimed, and claimed he had just stated a fact so it’s not a negative statement.

He also repeated criticism he voiced the night before about Clinton flying to Philadelphia Wednesday for a fundraiser with financial industry figures.

The comments come as the Sanders camp reportedly weighs whether to in fact launch a tough attack ad against Clinton in the closing days of the Iowa caucus race.

The New York Times reported Wednesday that the campaign has two ads ready to go – one, a positive spot; the other, an attack on Clinton’s Wall Street ties.

The Times report already is being used as a fundraising tool by the Clinton campaign, which is accusing Sanders of considering going back on past pledges not to run negative ads.

Hillary for America Iowa State Director Matt Paul, in a statement Thursday, described the potential plan as a “last-minute sneak attack from the Sanders campaign” meant to “plaster the Iowa airwaves in the days before the caucus with negative ads slamming Hillary Clinton.”

Sanders on Thursday continued to assert that the party brass are lined up against him. Asked if the establishment is starting to “tilt” away from him, he mocked the question.

"Tilt? Did you say tilt?" Sanders asked, adding that "of course the establishment is for Secretary Clinton."

Polls show Sanders and Clinton locked in a tight race for Iowa on Monday, while Sanders enjoys a comfortable margin atop most polls in New Hampshire, which votes the following week.

Thursday’s breakfast was hosted by Bloomberg Politics

Fox News’ Ed Henry contributed to this report.