European leaders vowed to redouble their support for Ukraine on Wednesday, amid fears that President Trump could stop or cut back on sharing military intelligence with Ukraine in its war with Russia.

President Volodymyr Zelensky of Ukraine on Wednesday referred to what he called recent “difficulties” with partners during a meeting in London with Prime Minister Andy Burnham of Britain. Mr. Zelensky did not offer details, but said he would talk with Mr. Burnham about intelligence sharing and Starlink, the satellite company owned by Elon Musk that has been crucial to its military.

He said there had been “a lot of different surprises” that wouldn’t be expected “when you have real partnership, and we count on partnership with the United States.”

On Wednesday, there was a sudden restriction of Ukraine’s access to a military version of the Starlink system, which is paid for by the Pentagon, security officials said. The loss of that access has not been explained.

The prospect of a disruption in the security relationship with the United States — which has enabled Ukraine to attack with precision and defend against incoming missiles and drones — rattled European officials, nearly five years into the war.

Verbal clashes between Mr. Trump and Mr. Zelensky in recent days have further frayed nerves, raising concern about how Ukraine could continue to defend itself against Russia if it were to lose U.S. intelligence.