Donald Trump. REUTERS/Dominick Reuter Real-estate magnate Donald Trump won't give evidence for his most explosive claim on the presidential campaign trail.

The Republican businessman has been generating waves of headlines and a storm of controversy by accusing the Mexican government of sending "rapists" and other criminals to the US. Businesses and others called the remarks offensive and cut ties with him as a result, but Trump insists he's simply telling the truth about a serious problem.

Trump was pressed for evidence Wednesday on MSNBC's "Morning Joe" but he would only say he had "sources" who told him about Mexico's actions.

"I've heard it from five different sources," he said.

Journalist Mark Halperin asked Trump to name his sources.

"I'll reveal my sources when you reveal your sources, Mark," Trump replied. "I have a lot of information on it and so does everyone else. And you probably do, too. And for some reason, they don't want to put out this information."

In the same interview, Trump also doubled down on his accusations against the Mexican government.

"You look at thousands of instances where illegals are coming in. And it's a crime wave. And frankly, Mexico doesn't care from the standpoint that they don't want to house these people for a long time period of time in their prisons. They say, 'Let the United States take care of them. Let the United States put them in their jails. Why should we pay for it?' And believe me, it's happening, and it's happening big league," he said.

Trump's claim about Mexico's plot to send criminals to the US first drew notice during his June 16 presidential campaign launch, where he railed against illegal immigration with heated rhetoric that has since been debated, defended, or attacked by all of the other presidential candidates. But instead of backing off, the real-estate developer embraced the controversy and has subsequently surged in the polls.

However, PolitiFact reported that a "range of immigration experts" have said there is no evidence to support Trump's claim.

Watch Trump's "Morning Joe" interview below: