Republican presidential front-runner Donald Trump said Wednesday that his proposed wall across the U.S.-Mexico border would be completed within two years.

"I would say it would be complete within two years from the time we start, we'll start quickly," Trump told Fox News' Sean Hannity at a town hall in Pittsburgh, Pa. "We'll start quickly, and it will be a real wall. It will be a real wall."

The self-imposed deadline was the most detail Trump has offered about his controversial proposal aimed at preventing illegal immigration. At one point, the crowd at the Soldiers & Sailors Memorial Hall began chanting "Build the wall! Build the wall!"

Trump followed that outburst with a call-and-response, asking the crowd "Who's gonna pay for the wall?" 

After the crowd responded, "Mexico!", Trump told Hannity, "They'll pay in one form or another."

Trump also accused Colorado Republican officials of changing the rules of the state’s convention to select delegates for this summer's national convention in Cleveland in response to his candidacy. 

“When I went into the race, which was in the middle of June—after that, they changed the whole thing in Colorado,” Trump said. “I would’ve done great in Colorado [if they didn’t] have this arcane [delegate] system that nobody understands.

“My delegates went there, they wouldn’t put them on the list, then they even did “Never Trump, Never Trump,” the real estate mogul added, referring to a now-deleted tweet from the state party’s official Twitter account that included the hashtag popular among Trump's detractors. The Colorado GOP blamed the miscue on “unauthorized access” in a later tweet.

Trump also criticized April 26’s Pennsylvania primary. Voters there will award 17 delegates to the statewide winner and 54 additional delegates will be elected directly by the voters. But ballots will not identify which candidate each of the additional 54 delegates have pledged to support. Some of the delegate names will be recognizable local officials, while others may be less-identifiable to voters.

“I could win Pennsylvania by a landslide…get 17 delegates, and somebody else could get 35 or 40, and they didn’t even win—but they have connections to the machine. It’s not right,” Trump said. "We have to bring the voter back into it."

Trump also touched on his meeting earlier Wednesday with Fox News anchor Megyn Kelly, with whom he has carried on a months-long dispute. 

"She was very, very nice," Trump said. "Maybe it was time or maybe she felt it was time. I give her a lot of credit for doing what she did."