The Pentagon has given leading US defence contractors 21 days to explain how they will accelerate weapons deliveries and expand production, as five months of war with Iran deplete stocks of key missile interceptors.

“Years-long development cycles are not acceptable,” Deputy Defence Secretary Steve Feinberg wrote in a 5 August memo obtained by The Washington Post. “We must dramatically accelerate our program schedules and expand our production capacity now.”

The memo instructed industry leaders to propose “significantly faster, more aggressive delivery schedules” or increased production for critical weapons. The department also wants companies to identify investments and factory expansions that could raise output.

Pentagon spokesman Sean Parnell confirmed on Saturday that the directive was genuine. He said the department was increasing munitions purchases to provide “the weapons our warfighters need at the pace the threat demands”.

Parnell said the effort had been accelerated during the past week but described it as part of a wider attempt to modernise the military and rebuild the US defence industrial base that began before the conflict with Iran.

President Donald Trump has disputed reports that the United States faces a shortage. He wrote on Truth Social on Thursday that the country had “massive amounts” of weapons and that further supplies were being manufactured and delivered as required. He provided no inventory figures.

The Pentagon has not publicly confirmed detailed figures for its interceptor holdings. Estimates published by the Center for Strategic and International Studies, a Washington think tank, indicate that the number of Patriot interceptors fell from about 2,330 before the war to 1,030 when a ceasefire took effect in April.

Following further fighting, the Patriot stockpile was estimated at between 759 and 827 interceptors — at least 65% below its pre-war level.

CSIS estimated that THAAD interceptor stocks fell from 452 before the conflict to between 232 and 262 by the April ceasefire. Subsequent deliveries raised the estimated total to between 234 and 278, still at least 38% lower than before the war.

The think tank said reduced inventories could force US forces and regional allies to conserve interceptors by launching fewer of them against incoming Iranian missiles and drones. That would increase the risk of some weapons penetrating air defences, it said.

The Pentagon had already taken steps to expand production. On 3 August, it announced agreements worth more than $3bn with Lockheed Martin and Northrop Grumman to increase manufacturing capacity for Patriot and THAAD components.

The department said the arrangements could allow Patriot production to triple and THAAD production to quadruple. They include creating a second supplier for Patriot solid rocket motors and expanding the manufacture of ignition devices and THAAD structural components.

Lockheed Martin was also awarded a seven-year contract valued at up to $58.62bn for PAC-3 Missile Segment Enhancement interceptors. The company said the agreement would support a tripling of production capacity by the end of 2030.

Some of the expansion plans will require congressional funding. A defence spending measure remains stalled as lawmakers dispute the administration’s military operations against Iran and the scale of its proposed Pentagon budget increase.

Parnell said Feinberg’s directive would inform the department’s funding request for the 2028 financial year. Contractors are expected to submit their acceleration plans by 26 August.