LONDON — Ukrainian leaders are concerned about the United States’ wavering support and have urged local manufacturers to boost self-sufficiency as a hedge, though air defense remains a complex bottleneck, according to the Ukrainian defense-procurement chief.

“We are very much concerned about that. It is something that’s kept us awake six months ago for sure,” Arsen Zhumadilov, director of the Defense Procurement Agency of Ukraine, told reporters on the sidelines of the DSEI trade show here last week.

Since taking office in January, President Donald Trump’s view on U.S. assistance to Ukraine has fluctuated considerably. In March, his administration suspended delivery of all American aid, prompting Ukrainian President Volodymyr Zelensky to say that the end of the war felt “very far away.”

Trump responded on his Truth Social media platform, calling Zelensky’s assessment “the worst statement” and warning that the U.S. “would not put up with it for much longer.”

By July, following a major Russian attack on Ukrainian cities, Trump shifted his position again. At a press conference, he announced plans to send additional weapons, stating, “They’re getting hit very hard now. I am disappointed that President Putin has not stopped.”

America’s stance has created pressure on local defense companies to be more self-reliant and produce more, Zhumadilov said. This comes at a time when Ukraine’s industry is already facing strains stemming primarily shaky supply chains, especially in obtaining critical components.

Zhumadilov highlighted air defense as a category of weapons that “cannot be as easily procured or produced” by the country’s national industry, at least to the extent “that would cover the whole needs we have.”

In contrast to other recent defense shows, Ukraine did not have a significant presence at DSEI. The country is hosting a similar event, the Defense Tech Valley investment summit, on Sept. 16-17 in Lviv.

The Ukrainian military-procurement boss noted that one of his priorities in attending the London fair was to shop for systems and components that remain hard to source locally.

“Some components are still scarce … which we need to import, as we cannot develop those capacities very quickly locally in Ukraine. … We want a better understanding of how we can make sure our contracts with producers don’t get de-prioritized because of some political or commercial reason,” he said.

Elisabeth Gosselin-Malo is a Europe correspondent for Defense News. She covers a wide range of topics related to military procurement and international security, and specializes in reporting on the aviation sector. She is based in Milan, Italy.