Andy Burnham has said he plans to travel to the US next month to join European leaders lobbying Donald Trump to supply Ukraine with Patriot missiles.

The UK prime minister told Bloomberg he was “looking forward to going to New York” in September, which is when the UN General Assembly will meet. He said details of the trip were not “fully confirmed” but it was “likely” to go ahead. The trip would be Burnham’s first US visit since becoming prime minister in July.

During Burnham’s first trip to Kyiv as prime minister, on Monday, he reiterated the UK’s “unwavering” support for Ukraine. Ukraine in turn handed over what officials have called a “goldmine” of battlefield data to help bolster British security.

In a meeting with the Ukrainian president, Volodymyr Zelenskyy, Burnham reiterated there would be “no change in the UK’s steadfast support” for Kyiv. He also urged Ukraine’s allies to send more interceptor missiles to Kyiv as it struggles under continued Russian bombardment, and co-chaired his first coalition of the willing meeting, where he said the group was doing “everything we can” to “dig into our own stocks and help others dig into their stocks”.

Zelenskyy has repeatedly pleaded for more US-made Patriot interceptor missiles in recent months as Kyiv’s stocks have diminished. Supplies of Patriots have been diverted to the Middle East since the outbreak of the US’s war with Iran, with Ukraine receiving significantly fewer missiles this year than in previous years.

During the interview with Bloomberg, Burnham said he felt “really confident” the problem was “fixable”, but added: “There are other players who could help in the mix who we have influence with. It’s probably going to be a solution that involves a lot of layers and a lot of negotiation.”

Russia has sought to capitalise on the shortage by stepping up its ballistic missile strikes, killing at least 23 people and wounding more than 100 in the past three days.

During his bilateral talks with Zelenskyy, Downing Street said Burnham had stressed the “strength of unity” among coalition of the willing countries.

A No 10 spokesperson said: “It had been an honest and productive conversation during the coalition of the willing, the leaders agreed, and it was clear the international community needed to step up and ensure Ukraine got the support it needed to defend itself from Russia’s barbaric attacks going into the winter.

“The prime minister emphasised the strength of unity among coalition members and reiterated that there would be no change in the UK’s steadfast support.

“That was further symbolised by the announcement that the UK had agreed that defence firm MBDA could release classified information on UK components for the long-range missile, Scalp, the prime minister said.”

Burnham and Zelenskyy had also signed an agreement to give the Ministry of Defence, working with selected British companies, access to Ukraine’s “Avengers” AI database, Downing Street said.

The deal is expected to help the UK learn from Ukraine’s experience on the battlefield and develop AI-powered solutions to national security challenges in both countries.

A Kremlin adviser has suggested UK factories producing drones for Ukraine could come under attack from “unknown sources”, after Britain’s agreement to share long-range missile blueprints with Kyiv.

Andrei Fedorov, a Russian former deputy foreign minister, told BBC Newsnight he could not “100% exclude” the prospect of “semi-military” action against Britain.

Fedorov said: “Sooner or later, there might be not only verbal, but maybe some visible reaction from Russia towards the UK.”

Asked to elaborate, he said: “There are different discussions how it should look like – it might be so-called technical reaction, maybe some hackers attack from unknown source, not from official level of course. There might be different political steps and I cannot exclude 100% that there might be some semi-military, for example.”

Pressed to define “semi-military” he said: “For example, something might happen with enterprises, with the factories which are producing drones for Ukraine, etc etc.” Asked whether this meant British factories being attacked militarily by Russia, he said: “They could be attacked, not by Russia, but by … from unknown sources.”