Gov. Christie on Monday refuted Donald Trump's claim that thousands of people in New Jersey had celebrated on Sept. 11, 2001, in stronger terms than when he had said he didn't recall the scene described by his rival.

"It didn't happen," Christie told reporters in New Hampshire. "The fact is, people can say anything, but the facts are the facts. That did not happen in New Jersey that day and it hasn't happened since."

The remarks drew Christie into Trump's crosshairs. The GOP frontrunner – who until Monday hadn't devoted much energy to attacking Christie – said the governor had been "very weak" in his previous response to the scene Trump says he witnessed on Sept. 11.

A little more than a week earlier, Christie had said "I don't recall" thousands in Jersey City cheering the collapse of the World Trade Center, as Trump had claimed.

"I do not remember that, and so it's not something that was part of my recollection," Christie said Nov. 22, after describing how Sept. 11, 2001 was a "harrowing day" for him personally. "I think if it had happened, I would remember it, but, you know, there could be things I forget too. But I don't remember that, no."

Trump had said during a Nov. 21 rally in Birmingham, Ala., that "thousands and thousands of people" in Jersey City "were cheering as that building was coming down." He repeated in a subsequent interview that "it was on television. I saw it. … There were people that were cheering on the other side of New Jersey, where you have large Arab populations."

Local officials have rejected that throngs of Muslims in New Jersey were cheering after Sept. 11, as did the former New Jersey attorney general who served during the attacks. The Washington Post's Fact Checker gave Trump four Pinocchios for the remarks.

Asked Monday if he would say "definitively" that thousands hadn't celebrated in New Jersey on Sept. 11, Christie said, "Yeah, I said that. People micro-analyze every word."

"I wanted to qualify it that day, not that I thought it happened, but just to remind people that that was a very emotional day for me. … It wasn't me trying to hedge anything," Christie said.

Trump – who has refused to back down from his claims – had a different take on Christie's comments Monday. "He didn't say that the other day," Trump told reporters in New York. "He was very weak the other day. The other day he said it like, well, he doesn't know, and now I guess he feels a little bit emboldened. He must be careful with what he says."

It wasn't Trump's only dig of the day at Christie. He took to Twitter earlier Monday to bash the governor, who was in New Hampshire collecting the endorsement of a prominent GOP activist, a day after getting the backing of the New Hampshire Union Leader newspaper.

"How is Chris Christie running the state of NJ, which is deeply troubled, when he is spending all of his time in NH?" Trump wrote. "New Jerseyans not happy!"

Asked in a CNN interview about the tweet, Christie quipped, "I'm just so glad to be noticed by Donald. Isn't that nice?"