By Tom Kludt

PHILADELPHIA (CNN) -- Donald Trump says he was only kidding when he appeared to encourage Russian intelligence agencies to find Hillary Clinton's thousands of deleted emails.

"Of course I'm being sarcastic," Trump said in an interview on Fox News that aired Thursday morning. "You have 33,000 emails to lead it, and the real problem is what was said on the emails from the Democratic National Convention."

Trump was referring to the recent hack of the Democratic National Committee, which led to the publication of thousands of emails on WikiLeaks. The emails showed officials criticizing Bernie Sanders during his primary campaign against Hillary Clinton, a time when the DNC claimed it was neutral in the race.

A US official said Thursday there is "little doubt" Russia was behind the DNC hack, prompting some to suggest that Moscow is trying to tilt the election in Trump's favor. In an interview on Tuesday, President Barack Obama said it is "possible" that Russian President Vladimir Putin is trying to bolster Trump's chances.

Trump campaign chairman Paul Manafort dismissed those claims as "crazy." Trump said in a tweet on Tuesday that Democrats were simply trying to "deflect the horror and stupidity of the Wikileakes (sic) disaster."

But at a press conference on Wednesday in Doral, Florida, Trump re-ignited the controversy with what appeared to be a challenge to Moscow.

"Russia, if you're listening, I hope you're able to find the 30,000 emails that are missing," Trump said, referring to the emails on a personal server that Clinton did not hand over to the State Department. "I think you will probably be rewarded mightily by our press."

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