While there was no official US confirmation of military assistance to Ukraine, Zelensky said afterwards that Trump had agreed to give Ukraine licences for domestic production of Patriot missiles.

“He accepted that he will give us licences,” Ukraine’s leader told Fox News. The BBC asked the White House for comment.

On his DC visit, Zelensky also met with leaders from the behemoth US weapons manufacturer Lockheed Martin.

In a statement on X, which was accompanied by photos of himself posing with company executives, he wrote: “We talked about our joint capabilities regarding Patriots and other systems.

“Our teams are already working on specific solutions to move to joint production as quickly as possible.”

Zelensky’s last stop would be the US Capitol, where he met dozens of senators in another closed-door meeting ahead of a crucial vote on a new package of sanctions on Russia.

He stood in a crammed hallway after the meeting and told a gaggle of reporters that Patriot systems were discussed here, too, and said passing the sanctions bill would send a “big signal to Europe, big signal to Ukraine, big support of our people”.

Zelensky was then ushered into the Senate chamber for a front-row seat as lawmakers voted overwhelmingly to advance the bill, a year after Graham, the late US senator, co-authored it.

If the Senate gives final approval to the bill, it will move to the House of Representatives, which is in recess until September.

The Patriot is one of the few air defence systems able to intercept ballistic missiles, which Russia has increasingly used to bombard Ukrainian cities.

It can catch rockets with flight ranges of up to 1,000km (620 miles). One battery can simultaneously track up to eight targets and detect more than 100.

But it comes with a price tag – each missile for the Patriot is estimated to cost from $3m to $5m.

Zelensky and the Ukrainian army have previously said Ukraine needs 25 Patriot interceptor systems.

As well as beefing up Ukraine’s military, domestic production of Patriots would shore up Zelensky’s approval rating in the wake of recent protests over his decision to oust a popular defence minister.

The key question is where Ukraine might produce those systems away from the prying eyes of the Kremlin, and whether it could be done quickly enough to alter the balance of the conflict.