Joe Biden accused top-tier Democratic nomination rival Pete Buttigieg in blunt terms this week of pilfering his health care reform plan.

“He stole it,” the former vice president told reporters during a wide-ranging question and answer session aboard his campaign bus in Iowa on Monday. “It’s the Biden plan.”

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But the South Bend, Indiana mayor’s campaign pushed back, telling Fox News and other outlets that Buttigieg has been discussing his health care plans since he launched his presidential exploratory committee in January. They note that Buttigieg specifically mentioned his "Medicare for All Who Want It" plan more than two months before Biden officially declared his candidacy in late April.

They point to a Feb. 15 interview on PBS' "NewsHour" where Buttigieg said “there are some legitimate questions about the pathway to Medicare for All. The flavor that I prefer is what I would call Medicare for All Who Want It.”

“In other words, take a version of Medicare, or something like it, make it available as a public option on the exchange, and then if people like me are right that this will over time become the most efficient and preferred means, then this will be a very natural glide path to a single-payer environment,” the candidate explained at the time.

While Buttigieg has been discussing his plan for much of this year, he didn’t formally unveil his health care proposal until Sept. 19. Biden released his health care plan on June 15.

Biden calls for expanding the Affordable Care Act, the signature health care law created during then-President Barack Obama’s administration in which Biden served as vice president. Biden is pushing to add a “public option” that would allow people to select a government health insurance plan, while others could continue using their private insurance.

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Biden’s comments come as Buttigieg has soared in recent polling in Iowa and New Hampshire, the first two states to hold contests in the presidential caucus and primary nominating calendar.

Buttigieg is now firmly part of the top tier of candidates in both states, along with Biden and populist Sens. Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts. Sanders and Warren – the two progressives standard-bearers in the large Democratic presidential field – both strongly support a government-run Medicare-for-all type health care system.

Asked during his interview aboard the bus whether Buttigieg now had the enthusiasm, he again scoffed. “No, he doesn’t have the enthusiasm and the moderate — moderate plan. It’s the Biden plan.”

And Biden, who’s received intense media scrutiny since even before he launched his campaign, scolded reporters for allegedly going too easy on Buttigieg. He said that the media would have heavily criticized him if he had copied another rival’s plans.

“What would you have done to me? You’d have torn my ears off,” the former vice president said.

Biden’s been asked numerous times about Buttigieg during his bus tour, which kicked off during the Thanksgiving holiday weekend. But his critical comments on Monday were his strongest to date.

Fox News reached out to the Buttigieg campaign, but top officials passed on directly responding to the former vice president’s jabs.

Biden also took aim at Warren, dismissing her rise in the polls during the summer and autumn.

“Look at the polling everywhere. Tell me. Tell me where the polling has manifested itself,” Biden argued. “She lives in Massachusetts, she’s invested millions and millions of dollars in New Hampshire, why shouldn’t she be known there?”

While the Warren campaign has spent generously to build a formidable organization and place plenty of boots on the ground in New Hampshire, campaign spokesman Chris Hayden told Fox News that "our campaign is not on air in New Hampshire, and we didn't run any TV ads during her 2018 re-election."

Fox News' Tara Prindiville and Madeleine Rivera contributed to this report.