Washington DC - White House budget chief Russell Vought refused to provide lawmakers with data or even an estimate of on the total cost of President Donald Trump's war on Iran.

During his testimony to the House Budget Committee on Wednesday, Vought claimed the administration didn't even have rough number to share.

"I don't have a ballpark for you," he said.

Vought appeared before the committee to testify about Trump's request for a record increase in military spending as part of next year's budget.

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"We're not ready to come to you with a request; we're still working on it," Vought said of a potential funding request to support the ongoing Iran war. "We're working through to figure out what's needed in this fiscal year versus next fiscal year."

During an interview with Harvard University's Kennedy School earlier this month, an expert in public finance suggested that the unprovoked war on Iran will ultimately cost US taxpayers up to $1 trillion.

"Wars always have a long tail of costs," Professor Linda Bilmes warned in a statement to Fortune. "Wars take the cost to go on for longer than we expect, and some of these costs are very consequential."