CLEVELAND — As Donald Trump once again warned his supporters on Saturday that voter fraud is rampant and could cost him the election, he wondered aloud if he is receiving any of the fraudulent votes.

"Maybe they'll vote for Trump, I don't know, maybe I shouldn't be saying that," the GOP presidential nominee said at a Saturday night rally in a convention center near the airport here. "I may be hurting myself, you're right. You're right. Maybe they're going to vote for Trump. All right, let's forget that. It's okay for them to do it."

His tone was joking — but Trump's comments follow several days of serious allegations that the system is "rigged" against him and that rampant voter fraud could cost him the election. He has claimed that Democrats are voting using the registrations of people who have died and that undocumented immigrants are illegally voting, even though there is no evidence that such fraud is widespread. At the rally Saturday, he also suggested that some people are voting more than once by visiting several polling locations.

"There is the issue that everybody says, 'Oh, oh, it doesn't take place,' " Trump said. "Are these people playing games with us? Right? 'Oh, it doesn't take place.' These are the people that negotiate our trade deals. These are the people that don't know what's going on in real life or these are the people that are just playing games with you. There is the issue of voter fraud. Isn't it amazing how they say, 'There's no voter fraud.' Folks, it's a rigged system, and it's a rigged election, believe me."

Trump also continued his ongoing attack on his rival, Hillary Clinton, and questioned why the Democrat did not stop the formation and strengthening of the Islamic State terrorist group.

"When will she take responsibility for all of the death and suffering and bloodshed she caused all around the world?" Trump said. "Look at what she's done. When will she apologize for all of the people her decisions have gotten killed?"

And Trump yet again cast suspicion on refugees from Syria who are fleeing a bloody civil war. He accused Clinton of wanting to have "an open border with the Middle East," something that Clinton has never called for.

"This is going to be the great Trojan horse — and you have to say I've been very good at predicting things," Trump said. "So let me state this as clearly as I can: If I'm elected president, I'm going to keep radical Islamic terrorists the hell out of our country."

The crowd cheered and then began to chant: "USA! USA! USA! USA!"

What Donald Trump is doing on the campaign trail

MANCHESTER, NH - NOVEMBER 7: Republican presidential candidate Donald Trump speaks during a campaign event at SNHU Arena in Manchester, NH on Monday November 07, 2016. (Jabin Botsford/The Washington Post)