(CNN) A top Pentagon official testified Wednesday that Ukrainian officials knew as early as July 25 there was an issue with US aid to the country, undercutting a key Republican rebuttal to accusations of a "quid pro quo."

In their defense of President Donald Trump, Republicans have alleged no bribery could exist if the Ukrainians weren't aware the aid was being held.

But Laura Cooper, the deputy assistant secretary of defense for Russia, Ukraine and Eurasia, testified as part of the House impeachment inquiry that some members of her staff recalled receiving queries about the aid from Ukrainian officials on July 25 -- the same day as Trump's much-scrutinized phone call with the Ukrainian President.

"What is going on with Ukrainian security assistance?" one Ukrainian contact emailed a member of her staff, Cooper recalled.

Laura Cooper, left, David Hale, right

Cooper couldn't say for certain whether the Ukrainian check-ins came because they were aware a hold was in place on the aid. But when asked if it could have just been a regular inquiry about the assistance package, Cooper responded: "It's my experience with the Ukrainians they would call about specific things, not just generally checking in on the assistance package."

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