Washington (CNN) President Donald Trump on Tuesday defended his unsubstantiated assertion that "unknown Middle Easterners" are traveling in a migrant caravan traveling north to the United States from Central America, but admitted "there's no proof of anything."

"They could very well be," Trump reiterated during a bill signing in the Oval Office, referring to Middle Eastern individuals embedded in the caravan. "I have very good information."

However, pressed for the proof of Middle Eastern individuals in the caravan by CNN's Jim Acosta, Trump said "there's no proof of anything."

"There's no proof of anything but they could very well be," Trump said.

On Monday, Trump tweeted "criminals and unknown Middle Easterners are mixed" into the migrant caravan moving toward the United States. He called this a "national emergy" (sic).

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