Washington (CNN) President Donald Trump asked his acting chief of staff Mick Mulvaney to put a hold on millions in military aid to Ukraine roughly one week before a call with the Ukrainian president in which he pressured the country to investigate former Vice President Joe Biden's son, two senior administration officials said on Monday.

Trump, who was in the middle of a broad review of foreign aid programs when he singled out Ukraine specifically this summer, was primarily concerned with "corruption" in Ukraine and Europe shouldering more of the financial burden for supporting Ukraine's defense, according to one of the officials.

News of Trump's order to withhold aid to the Ukraine ahead of his July 25 call may trigger questions -- and speculation -- about the President's motive in doing so.

Trump had ordered a hold on nearly $400 million of military and security aid to Ukraine at least a week before the call in question, US officials familiar with the matter tell CNN. The Washington Post first reported the figure.

The administration was looking at harnessing multiple foreign packages, several aides believed, when Trump took a special interest in Ukraine, at times railing about how the country wasted money in his eyes. This surprised several staffers because, as CNN has reported, Trump had not been interested in engaging with Ukraine in the past, believing Ukraine was a corrupt country that wasn't committed to reform.

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