The US and the European Union must make it clear to Putin that he has stepped far outside the bounds of civilised behaviour, and that this carries a steep price in international standing and in economic relations, The New York Times said in an editorial Sunday.
It also said that the Western powers must provide prompt and substantial assistance to the Ukraine government, whose treasury was left bare by ousted president Viktor Yanukovych's government.
According to the editorial, Putin's claim of an immediate threat to Ukrainian Russians is baseless.
"There were some scuffles in the industrial cities where Russians predominate, but nowhere were Russian speakers or Russian interests seriously threatened -- certainly not in Crimea, where Russians are the majority and the Russian Federation has military bases," it said.
President Viktor Yanukovych fled knowing well that he would not last long given the public fury over the killings in Kiev's Independence Square and expose of his thievery, the editorial stated.
"If he thought he had a shred of credibility left, he should have stayed and faced the music," it said.
"Putin knows this; his defence of the ousted government is a pretext to tighten Russian control over Crimea, buttress his claims to special rights over what he calls Russia's 'near abroad', and to humiliate Ukraine, the way he humiliated Georgia in 2008 for looking wistfully westward."
The editorial also suggested that Obama, NATO and the European Union should seriously consider what else they can do if Putin escalates his intervention in Ukraine.
It said Putin could demand more autonomy for Crimea, or annex it outright, or let the Crimean Russians declare "independence", the way the breakaway Georgian provinces of Abkhazia and South Ossetia did.
Putin could deepen Ukraine's economic woes by raising prices for gas and tightening border controls, the daily said.
The editorial, however, criticises the Ukraine's opposition for the way Yanukovych's government was thrown out.
"The victorious opposition should have known how critical it was to reassure all groups in that country that their rights would be respected in any new order; instead, one of the Parliament's first actions was to abolish a law that ensured a legal status for Russian and other minority languages, thus raising fears among Russian speakers that Ukrainian nationalists were taking over," it said.