MUNICH — Vice President Kamala Harris told the Munich Security Conference on Saturday that the Western alliance faced a “defining moment” in the Ukraine crisis and warned Russia’s leaders that if they invaded Ukraine, the United States and its allies would target not only financial institutions and technology exports to Russia, but also “those who are complicit and those who aid and direct this unprovoked invasion.”

The speech was the first time Ms. Harris has stepped into the hurricane of the diplomacy and signaling surrounding a high-stakes international crisis, so every word — and how she delivered it — was watched with care.

Her text hewed closely to the message that Secretary of State Antony J. Blinken delivered on Thursday at the United Nations. “This playbook is all too familiar to us all,” she said of the events unfolding near Ukraine’s borders. “Russia will plead ignorance and innocence. It will create false pretexts for invasion, and it will amass troop and firepower in plain sight.”

“Russia continues to claim it is ready for talks, while at the same time it narrows the avenues for diplomacy,” Ms. Harris said. “Their actions simply do not match their words,” a phrase that French officials have also used in denouncing threatening posture by President Vladimir V. Putin of Russia.

The vice president met on Saturday afternoon with President Volodymyr Zelensky of Ukraine, who flew to Munich for a few hours at the moment his country faces the most acute threat of full invasion in its history. Several Biden administration officials expressed concern about his travels to Germany, saying that they expected Russia to claim he had fled the country. A few worried about whether Moscow would try to block his return.

But in meeting Ms. Harris and speaking at the conference, where he last appeared two years ago to talk about cracking down on corruption and bolstering the Ukrainian economy, Mr. Zelensky hoped to bask for a brief moment in the embrace of partners who have promised to aid him but have said they will not send troops to face the Russian military.

Ms. Harris argued in her speech that the crisis had driven NATO allies together. “As President Biden has said, our forces will not be deployed to fight inside Ukraine,” she said, touching on — but not exploring — the decision to leave the fighting to Ukraine’s own military. “But they will defend every inch of NATO territory.”

Later, the vice president added, “our strength must not be underestimated.”