BRUSSELS — Vice President Mike Pence told a rattled Europe on Monday that President Trump fully supported crucial European institutions — despite the president’s perplexing comments and occasional insults — and said he supported the firing of the national security adviser.

“The president did ask me to come here to Brussels, to the home of the European Union, and deliver an additional message,” Mr. Pence said while standing next to Donald Tusk, president of the European Council and a former prime minister of Poland. “So today it’s my privilege, on behalf of President Trump, to express the strong commitment of the United States to continued cooperation and partnership with the European Union.”

Asked for his response to the resignation of the national security adviser, Michael T. Flynn — whom the administration blamed for misleading Mr. Pence about the extent of his conversations with the Russian ambassador to the United States — Mr. Pence looked uncomfortable but said he supported Mr. Trump’s decision to ask for Mr. Flynn’s resignation.

“Let me say, I’m very grateful for the close working relationship I have with the president of the United States,” Mr. Pence said, adding, “I was disappointed to learn that the facts that have been conveyed to me by General Flynn were inaccurate.”