Mitt Romney's campaign is ramping up its criticism of chief rival Rick Santorum, with top surrogate and former New Hampshire Gov. John H. Sununu (R) questioning Santorum's "temperament" during a call with reporters Monday.

“Sen. Santorum really has lost his personal discipline and self-control in the process, lashing out at the press, and frankly, lashing out at his opponents,” Sununu said, according to the National Review.

“One of the most important things you need in a president is self-control and discipline. It is one thing to lose your temper at a New York Times reporter and it’s another to have to deal with the pressures of folks on the international stage and even opposing congressional leaders," he continued. "And you need discipline. You need self-control. You need to be able to handle your messaging and focus on it."

The remarks were in direct reference to an incident over the weekend in which Santorum accused a New York Times reporter of "distorting" his words.

The confrontation occurred shortly after a speech in Wisconsin in which Santorum said that primary rival Mitt Romney was "the worst Republican in the country to put up against Barack ObamaBarack Hussein ObamaOvernight Cybersecurity: What we learned from Carter Page's House Intel testimony | House to mark up foreign intel reform law | FBI can't access Texas shooter's phone | Sessions to testify at hearing amid Russia scrutiny Russian social media is the modern-day Trojan horse Trump records robo-call for Gillespie: He'll help 'make America great again' MORE."

"Pick any other Republican in the country," the former Pennsylvania senator said, according to The Associated Press. "He is the worst Republican in the country to put up against Barack Obama."

Times reporter Jeff Zeleny then asked Santorum if he thought Romney was actually the "worst Republican" to face the president — a question likely motivated by a campaign gaffe last week in which Santorum suggested that President Obama could be the preferable choice over Romney. 

"Quit distorting my words. It's bulls--t," Santorum said.

The former senator went on to say he was only referring to Romney's stance on healthcare.

"On the issue of healthcare, yes, that's what I was talking about," Santorum told reporters later on. "ObamaCare, as you heard me say."

But Romney's campaign mocked Santorum for the moment and said he was hurting Republican chances in the general election.

“Right now, what he is doing with his emotional outbursts, is just giv[ing] President Obama some sound bites, dragging the process out, and frankly, right now, he’s running on ego and emotion," Sununu said.

Santorum defended the comments Monday, asking supporters to donate the price of a Times subscription to his campaign and framing confrontations with reporters from the paper as a GOP rite of passage.

"I don't regret it at all," Santorum said during an appearance outside the Supreme Court, where he was protesting the president's healthcare reform legislation.

-This article was updated at 4:15 p.m.