Most of the costs are not budgeted for, meaning the Pentagon will need to request more funding soon, researchers say.

The United States-Israeli war on Iran is estimated to have cost Washington $3.7bn so far in its first 100 hours alone, or nearly $900m a day, driven largely by the huge expenditure of munitions, according to new research.

An analysis by Washington-based think tank the Center for Strategic and International Studies (CSIS) underlined the colossal cost of the war, which entered its seventh day on Friday, as the US attacks Iran with stealth bombers and advanced weapons systems.