US President Donald Trump's administration said it used $5.6 billion in munitions during the first two days of strikes against Iran in a report provided to US congressional committees, a source familiar with the information said on Tuesday.

Members of Congress, who may soon have to approve additional funding for the war, have expressed concern that the conflict will deplete US military stocks at a time when the defence industry was already struggling to keep up with demand.

Trump met executives from seven defence contractors on Friday as the Pentagon worked to replenish supplies.

The administration has not provided a public assessment of the cost of the conflict it launched on February 28 along with ally Israel.

More funding

Members of Congress have clamored for more information, including public testimony from officials about issues including how the conflict might affect the US military's readiness to defend the country.

Several congressional aides have said they expect the White House to soon submit a request to Congress for additional funding for the war.

Some officials have said the request could be for $50 billion, but others have said that estimate seems low.