The Pentagon has informed lawmakers that it requires about $80 billion in additional funding, largely to cover costs associated with the US military campaign against Iran, as President Donald Trump seeks a major increase in defence spending.

According to people familiar with the matter, Deputy Defence Secretary Stephen Feinberg briefed senators last week on the proposed funding and told congressional committees that the request had been submitted to the White House Office of Management and Budget.

The administration has yet to formally send the request to Congress.

Defence Secretary Pete Hegseth has also been meeting lawmakers on Capitol Hill to discuss the proposal, which comes amid growing scrutiny over Trump’s handling of the conflict with Iran and concerns over expanding military expenditures.

Senate Majority Leader John Thune said he expects the administration to submit a supplemental spending request and that lawmakers would assess support once it arrives.

“We need to make sure we’re doing everything we can to replenish and resupply munitions that have been depleted, not only because of Iran but previous operations as well,” Thune said.

The White House is seeking a record $1.5 trillion defence budget, nearly 50% higher than current spending levels.

Republicans hope to secure around $1.1 trillion through the normal appropriations process and another $350 billion through a separate measure later this year.

The Pentagon’s latest estimate is significantly higher than the $29 billion figure Hegseth provided lawmakers last month, though it remains below the initial $200 billion estimate floated at the start of the conflict.

Early assessments had put the cost of the war’s first week alone at $11.3 billion.

Democratic lawmakers have voiced strong opposition to additional military spending.

Senator Patty Murray criticised the administration’s approach, arguing that taxpayers’ money was being spent on a war many Americans oppose.

Senator Brian Schatz said he had found little support among Democrats for an Iran-related spending package and warned that the final cost could exceed the proposed $80 billion.

Some Republicans, however, defended the request, arguing that replenishing military stockpiles and boosting domestic defence production were essential.

Senator Jim Banks said the spending should be viewed as an investment in the US defence industrial base.

Senator Jack Reed, the top Democrat on the Senate Armed Services Committee, said any supplemental funding should be considered alongside broader negotiations on defence and non-defence spending.

Meanwhile, Senator John Hoeven said he has been working with the administration to combine the defence package with disaster relief funding for states affected by wildfires and severe weather, as well as assistance for farmers, arguing such a measure would stand a better chance of winning congressional approval.

Hegseth declined to comment on the proposal while leaving the Capitol on Monday.

During a Senate hearing last month, he defended the cost of military action, asking lawmakers: “What is the cost of Iran obtaining a nuclear weapon?”

He acknowledged that confronting Tehran’s nuclear ambitions carries financial costs, but said the administration considered them necessary.