"We've helped in many ways to create the problems that exist there. And to leave them alone in the manner that we're leaving them alone to me is just unconscionable," Sen. Bob Corker, the committee's senior Republican member, said on NBC television's "Meet the Press."
"I don't think Putin really believes we're going to punish them in that way," he said.
"If Russia does get away with this, I do think that there's a potential that a NATO ally is next. And, yes, there will be economic pain to Europe (under tightened sanctions). But it's time for them to lead as well."
President Barack Obama has said his administration is prepared to take further action against Russia if diplomatic efforts to destabilize the conflict fail.
More From This Section
Vice President Joe Biden plans to be in Kiev, the Ukrainian capital, on Monday and Tuesday to meet with government leaders and democracy advocates.
The Pentagon's press secretary, Rear Adm. John Kirby, has said that American officials are considering a range of additional measures to bolster air, maritime and ground readiness in Europe.
A Western official said yesterday that the US is considering deploying about 150 soldiers for military exercises to begin in Poland and Estonia.