Sen. John McCain called for massive military assistance to Ukraine Saturday, while warning that Russia's actions in its former Soviet neighbor could lead to unprecedented measures by the United States and it allies.
"Ukraine is going to need a long-term military assistance program from the United States," the Arizona Republican told reporters a Senate delegation visit to the Ukrainian capital, voicing what he said was a personal opinion.
"When (Ukrainians) ask for some modest means that can help them resist, I believe we should provide it... it's simply the right and decent thing to do."
His comments came shortly before Kiev accused Russia of invading a region in southeast Ukraine, neighboring Crimea.
McCain said he was "deeply concerned" about previous reports of Russian troops moving closer to Ukraine's eastern border and conducting snap military drill there, after having effectively seized Crimea at the start of the month.
He said an all-out Russian invasion of eastern Ukraine "will be a breach of such enormous consequence that the United States of America and our European allies will be contemplating action that we have not ever (contemplated) in our relations with Russia."
So far, Washington has vowed to impose travel bans and asset freezes on targeted Russians in what has turned into the worst East-West faceoff since the Cold War.
Ukraine is meanwhile headed for a breakup as southern Crimea prepares to vote on Sunday in a referendum that is widely expected to favour reattachment to Russia.
McCain however refused to accept reports that Kiev might sacrifice the Black Sea peninsula in exchange for keeping its eastern majority Russian-speaking region.
"The last thing we want to do is send any message to the people in Crimea that we have abandoned them," he said.
"We do not agree that (Russian President) Vladimir Putin has the license to invade a sovereign nation."
The US senators -- who met with Ukraine's new leaders and members of the Maidan protest movement in Kiev -- did not mince their words on the eve of the Crimean referendum, organized by the self-appointed pro-Moscow regional authorities but slammed as illegal by the new authorities in Kiev and foreign capitals.
McCain spoke of a "phony referendum" while his colleague Richard Durbin described a "Soviet-style election in Crimea. We know the outcome, we always knew the outcome of those elections long before they took place."
Ukraine on Saturday accused Russian forces of invading the village of Strilkove off the northeastern edge of the Crimean peninsula, and vowed to use "all necessary measures" to ward off the attack.