For months, Ukrainian officials have carefully navigated the turbulent partisan politics in the United States leading up to November’s elections, saying that they could work with either a Democratic or Republican administration.

But on Wednesday night, Mike Johnson, the Republican speaker of the House, called for Ukraine to fire its ambassador to Washington, accusing her of meddling in American election affairs.

In a public letter addressed to President Volodymyr Zelensky of Ukraine, Mr. Johnson demanded the dismissal of the Ukrainian ambassador, Oksana Markarova, citing her role in organizing a visit by Mr. Zelensky to an ammunition factory in Scranton, Pa. Mr. Zelensky toured the factory this week and thanked workers for manufacturing shells sent to his country’s embattled forces.

Mr. Johnson criticized the visit for taking place in a key battleground state in the company of Gov. Josh Shapiro, a Democrat who supports Vice President Kamala Harris in her presidential bid. The speaker noted that no Republicans were invited.

“The tour was clearly a partisan campaign event designed to help Democrats and is clearly election interference,” Mr. Johnson wrote in the letter on Wednesday.

The same day, James Comer, a Republican who chairs the House Oversight Committee, announced that he had launched an investigation into the visit, saying it was a partisan event paid for with taxpayer funds.