THE DESTRUCTION of a Malaysian airliner over Ukraine may not have been intended by Russia or the militants it has supported and armed. But their behavior since the downing of the plane has been a lesson in barbarity and morally contemptible statecraft. While its proxies, commanded by some of its own citizens, did their best to cover up the atrocity, the government of Russian President Vladi­mir Putin has denied the obvious, employing a blatantly mendacious propaganda campaign.

The tactics prompted angry statements Monday from President Obama and European leaders. But more Western rhetoric is not what is needed now.

Late Monday, rebels who control the region where the plane was downed finally appeared to be taking steps toward cooperating with the Malaysian government and other international authorities. Nothing, however, can compensate for the militants’ behavior in the four days after a Russian-supplied anti-aircraft battery on their territory shot down the airliner. According to numerous reports, they prohibited international investigators from reaching the site, haphazardly loaded bodies onto train cars and looted the personal effects of victims.

In Moscow, Mr. Putin disappeared from view after making a statement assigning responsibility for the downing to the Ukrainian government on the absurd grounds that Kiev had dared to fight back against the infiltrators dispatched and armed by his own regime. Moscow’s propaganda apparatus then swung into action, producing a blizzard of fake evidence and bizarre conspiracy theories to deflect responsibility. At a Defense Ministry briefing Monday, journalists were presented with concocted data purporting to show that the Malaysian flight could have been shot down by a Ukrainian warplane — a lie that is the more bold because of the ease with which it can be disproved.

It’s worth underlining that this rogue-state behavior is being practiced not by an acknowledged pariah nation but by an accepted member of the Group of 20 that aspires to be treated by the West as an economic and strategic partner. It follows the first forcible invasion and annexation of European territory since 1945, as well as a months-long covert campaign in which Russian military operatives, mercenaries and heavy weapons have entered eastern Ukraine.

GRABOVKA, UKRAINE - JULY 18: A man looks at debris from an Air Malaysia plane crash on July 18, 2014 in Grabovka, Ukraine. (Brendan Hoffman/Getty Images)

Both the United States and the European Union have been too tactical and too tolerant in responding to Russia’s new barbarism. On Monday, President Obama was still focused on “investigating exactly what happened” — even though the evidence of Russian responsibility is already abundant. He had nothing tangible to say about consequences. He and European leaders say their objective is a “cease-fire” in eastern Ukraine , though that would likely freeze in place the men and weapons Russia has sent there and make it virtually impossible for Kiev to regain control over the territory.

What’s needed is a broad strategy for putting a stop to Mr. Putin’s aggression and, where possible, rolling it back. That begins with sanctions designed to inflict damage on the Russian economy, such as the “sectoral” sanctions Mr. Obama and German Chancellor Angela Merkel threatened months ago but never deployed. Military measures are also necessary, including rapidly supplying the Ukrainian army with the material it has requested. It’s time to treat Mr. Putin’s Russia as what it has become — a dangerous outlaw regime that needs to be contained.