Ukrainian President Volodymyr Zelensky fired his ambassador to the United Kingdom on Friday.

The ambassador, Vadym Prystaiko, had criticized Zelensky over his reaction to recent remarks by British Defense Secretary Ben Wallace, who had suggested Ukraine had not expressed sufficient "gratitude" for Western financial support.

Prystaiko said Zelensky's response to Wallace amounted to "unhealthy" sarcasm.

A statement published Friday on the Ukrainian presidency's website confirmed Prystaiko's dismissal but did not provide a reason.

The tension began at a NATO summit in Lithuania earlier this month, when Wallace said that "whether we like it or not, people want to see gratitude for the West's military contributions to Ukraine's war effort.

"I said to the Ukrainians last June, when I drove 11 hours to be given a list -- I'm not Amazon," Wallace said.

When asked about those remarks by a reporter at the NATO summit, Zelensky was nonplussed.

"I just don't know what he means. How else should we thank him? Well, let him write to me and tell me how I need to thank people so that we can be fully grateful. We can also wake up in the morning and thank the minister personally."

Prystaiko was interviewed about the exchange the following day on Sky News, where he was asked whether there was a "hint of sarcasm" in Zelensky's response to Wallace.

Prystaiko conceded there was "a little bit of sarcasm," and went on to say: "I don't believe this sarcasm is healthy."

"We don't have to show the Russians that we have something between us. They have to know that we are working together. If anything happens, Ben can call me and tell me everything he wants," said Prystaiko.

CNN has attempted, unsuccessfully, to reach Prystaiko for comment.