The figure, revealed during a budget hearing on Capitol Hill, is about $4 billion higher than the department's previous estimate given two weeks ago.

Hegseth, Joint Chiefs Chairman Dan Caine and Pentagon finance chief Jules Hurst III were asked about the war's price tag during testimony on the administration's $1.5 trillion 2027 defense budget request.

"At the time of testimony... it was $25 billion," Hurst said, referring to Hegseth's April 29 estimate.

"But the joint staff team and the comptroller team are constantly looking at that estimate, and so now we think it's closer to 29," he said -- citing updated "repair and replacement of equipment costs" and broader operational expenses.

Democrats and other critics of the war have questioned the Pentagon's calculations, suggesting the true cost -- including damage inflicted by Iran -- could be far higher.

Pressed on when Congress would receive a fuller accounting, Hegseth said the administration would request "whatever we think we need" separately from the Pentagon budget, without giving a timeline.

The testimony came as a fragile US-Iran ceasefire appeared increasingly shaky, with Trump warning Monday that the truce was on "life support" after rejecting Tehran's latest peace proposal.

Democrats used the hearing to hammer the administration over the ballooning cost of the war and what they described as a lack of transparency about US objectives.

"The question must be answered at the end: what have we accomplished and at what cost?" asked Rosa DeLauro, the top Democrat on the House Appropriations Committee.

- Weapons stockpiles -

The hearing marked Hegseth's first appearance on Capitol Hill since the White House formally notified Congress that hostilities launched by the United States and Israel against Iran on February 28 had "terminated."

Democrats, accusing Trump of waging war without congressional authorization, have repeatedly introduced measures to curb his war powers, only to be blocked by Republicans.

Democratic Senator Mark Kelly warned at the weekend that inventories of Tomahawk missiles, Patriot interceptors and other advanced weapons had been severely drawn down and could take years to replenish.

But Hegseth dismissed the concerns as "foolishly and unhelpfully overstated."

Hegseth and Caine faced a second round of questioning before a Senate panel after their House appearance, and there were anti-war protesters at both hearings.

In the Senate, Democrat Patty Murray said the administration's cost estimate appeared "suspiciously low" because it did not account for damage to US facilities, citing reports that Iran struck at least 228 structures or pieces of equipment at military sites.

Virginia Burger, senior defense policy analyst at the Project On Government Oversight, suggested the administration might be understating the war's true cost by "tens of billions" of dollars.

"The only way to know what the discrepancy is and what this war is truly costing taxpayers is if the Pentagon provided Congress with a detailed breakdown of the costs," she said.

"Without seeing the numbers, we're forced to wonder if the Pentagon is engaging in mathematical tricks and selective inclusion to make the official cost estimate as low as possible."

Hegseth declined to provide a damage estimate, but argued -- as he has repeatedly since the war began -- that the cost of Iran obtaining a nuclear weapon would be far greater.

Trump has repeatedly claimed US air strikes "obliterated" Iran's nuclear program last year, despite intelligence assessments indicating Tehran was a decade away from developing a missile capable of threatening the United States.