US Defence Department officials have told senators in a closed-door briefing that they estimate the first six days of the war in Iran cost more than $11.3 billion, NBC News reports, citing three sources familiar with the briefing.

Senator Chris Coons told reporters that he believes the amount is even higher, as the current figure does not include every aspect of the war.

“I expect that the current total operating number is significantly above that,” Coons was quoted as saying. “If all you’re looking at is the replacement cost for the munitions used, it’s already well beyond $10 billion.”

Reached for comment, a Pentagon spokesperson told NBC: “We do not comment on closed-door discussions or matters. Regarding the cost of Operation Epic Fury, we won’t know the cost until the mission is complete.”