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.”