Vice President Kamala Harris on Friday heralded NATO unity during the escalating Ukraine crisis and warned Russia that the U.S. and Western allies stood ready to respond with tough sanctions if President Vladimir Putin moves forward with an invasion of Ukraine.

In a meeting with NATO Secretary-General Jens Stoltenberg as the annual Munich Security Conference got underway, Harris thanked the alliance for "all that you have done" throughout the crisis.

"We remain, of course, open to and desirous of diplomacy, as it relates to the dialogue and the discussions we have had with Russia, but we are also committed, if Russia takes aggressive action, to ensure there will be severe consequence in terms of the sanctions we have discussed," Harris told Stoltenberg. "And we know the alliance is strong in that regard."

Harris and her top national security aides huddled with Stoltenberg after President Joe Biden on Thursday in Washington warned that "every indication" suggests Russia is "prepared to go into Ukraine, attack Ukraine."

The U.S. now estimates that Russia probably has massed between 169,000 and 190,000 personnel in and near Ukraine, up from about about 100,000 on Jan. 30, said Michael Carpenter, the permanent U.S. representative to the Organization for Security and Cooperation in Europe.

In addition to troops along the border, in neighboring Belarus and in Crimea, he said the estimate includes Russian-led forces in eastern Ukraine and also internal security units deployed to these areas. It was unclear if these forces were included in the most recent estimate of 150,000 troops.