Answering questions at NATO headquarters, Ms. Hutchison suggested that the United States was getting ready to document Russian violations of the treaty based on new information “we have uncovered.”

“We are asking our allies for their suggestions on a way forward that would bring Russia into compliance, because that is our goal: Russia in compliance,” she said, comments that echoed past statements in the Obama and Trump administrations.

But Ms. Hutchison also warned that if Russia did not change course, the United States might field its own weapons, which would require going ahead with “a development phase that is not allowed by the treaty right now.”

Then she was asked to be more specific about “what kind of countermeasures you are considering.” Ms. Hutchison then uttered the words that the State Department spent most of Tuesday walking back.

“The countermeasures would be to take out the missiles that are in development by Russia in violation of the treaty,” she said. “So that would be the countermeasure eventually.”

Pressed further, Ms. Hutchison said her first choice was to get the Russian missiles withdrawn, adding that if the Russians did not relent “we would then be looking at a capability to take out a missile that could hit any of our countries in Europe and hit America in Alaska.’’

That last statement seemed to suggest an upgrade to missile defenses. But it is not clear that current missile defense technology could protect against medium-range missile attacks, and Russia — like the United States — is working on other missiles, called hypersonics, that do not follow a clear path to a target. Those may, in time, overshadow the missiles that are now part of the I.N.F. treaty debate.