Republican presidential candidate Donald Trump defended Russian President Vladimir Putin against accusations that he has assassinated political adversaries and journalists, responding to criticism from his rivals over his embrace of praise from the Russian leader.

"Nobody has proven that he's killed anyone. . . . He's always denied it. It's never been proven that he's killed anybody," Trump said on ABC's "This Week" on Sunday. "You're supposed to be innocent until proven guilty, at least in our country. It has not been proven that he's killed reporters."

On Thursday, Putin praised Trump during a wide-ranging news conference, calling him "talented without doubt" and "brilliant." Trump has embraced the remarks, drawing fire from critics such as Sen. John McCain, R-Ariz., who facetiously called the alliance "a match made in heaven." Trump welcomed Putin's praise, citing it as proof that a Trump administration would be able to work well with the Russians.

"If he has killed reporters, I think that's terrible. But this isn't like somebody that's stood with a gun and he's, you know, taken the blame or he's admitted that he's killed. He's always denied it," Trump added.

Trump also fired back at claims by Democratic front-runner Hillary Clinton that his anti-Muslim rhetoric has become fodder for recruiters of the Islamic State militant group, calling it "another Hillary lie." During a rally in Cedar Rapids, Iowa on Saturday, Trump said Clinton is "like a snake with no energy."

"Nobody has been able to back that up. It's nonsense. It's just another Hillary lie," he said on NBC's "Meet the Press" on Sunday, according to an advance transcript. "She lies like crazy about everything, whether it's trips where she was being gunned down in a helicopter or an airplane, she's a liar and everybody knows that. But she just made this up in thin air."

"Meet the Press" host Chuck Todd pressed Trump on his rhetoric, asking him,"If you knew your words were being used, would you change your language?" Trump dismissed the question.

"No, because I think that my words represent toughness and strength. Hillary's not strong. Hillary's weak, frankly. She's got no stamina, she's not nothing," Trump said. "She couldn't even get back on the stage last night." Clinton took a little time to return to the stage after the customary break midway through the Democratic debate on Saturday.

For his part, Democratic candidate Bernie Sanders knocked Trump's rhetoric in an interview on ABC's "This Week" on Sunday, accusing him of lying pathologically.

"I think, and I say this straightforwardly, I think you have a pathological liar there. ... I think much of what he says are lies or gross distortion of reality," Sanders said. "Nobody has seen a tape of thousands of people celebrating the destruction of the Twin Towers in New Jersey. It doesn't exist. And he keeps claiming it. That's called pathological lying."