Regular Russian troops are fighting in Ukraine, and it's a whole new game.

The capture of Russian paratroopers in eastern Ukraine, and the quiet burials of other Russian solders, provided enough evidence that the nature of the conflict had changed. Now, though, Ukrainian President Petro Poroshenko has officially announced that "Russian troops were actually brought into Ukraine."

A second front has been opened against the Ukrainian army in the rebellious Donetsk region. The Ukrainians were forced to give up the town of Novoazovsk on the Sea of Azov, not far from the strategic port of Mariupol, used by Kiev as the supply base for its anti-rebel operation. Ukrainian military commanders say Russian troops entered the town. Although such claims have been made before, there's more reason than ever to believe them today.

It's highly unlikely that the pro-Russian rebels, whom the better-equipped Ukrainian troops had confined to the cities of Donetsk and Lugansk, could have suddenly showed up at the Ukrainians' rear and attacked the seaside towns. The North Atlantic Treaty Organization, which had never before accused Russia of sending in troops, now says there are at least 1,000 Russian service members fighting in Ukraine.

Judging from anecdotal information about troops' funerals and from reports from the Russian Soldiers' Mothers' Committee, the Russian troops are elite airborne units. They will be the most formidable opposition the Ukrainian military has faced since the conflict began five months ago -- a far cry from the untrained local separatists, assorted war re-enactment enthusiasts and nationalist fanatics they've dealt with so far.

By rotating a few thousand elite troops in and out of Ukraine, the Kremlin can keep up the fighting indefinitely. Now that Russia's direct involvement is getting impossible to deny, a broader invasion becomes a possibility. Ukraine's understaffed, undertrained forces would be no match for the Russian army, in which Russian President Vladimir Putin has been making a major investment. In 2013, Russia was the third biggest defense spender globally, after the U.S. and China. As Ukrainian Prime Minister Arseniy Yatsenyuk correctly put it, Ukraine can "handle Russian terrorists but not the Russian army."

As a Russian, I get a sinking feeling when I think about my country winning this war. It is being fought against a peaceful, Russian-speaking people whose only transgression is a desire to be part of the European Union rather than a Russian client state. They even managed to topple a corrupt dictatorship -- a task in which the Russian people have failed. A military victory against Ukraine would bring Russia no glory and cost many lives.

"We can stop this," billionaire and former political prisoner Mikhail Khodorkovsky said today. "It's enough to just take to the streets and threaten a strike. The authorities will deflate immediately, they are cowardly." That may be true, but it's not likely to happen, because most people in Russia believe Putin's propaganda. Unless the death toll mounts so that everyone knows a dead or injured soldier, this is not a war that protests inside Russia are likely to stop.

Putin's decision to escalate signals the failure of Western sanctions. If anything, the sanctions have strengthened Putin's resolve to get his way and consolidated his popularity among conservative, nationalist voters, expanding his support base at home. If Putin ever cared about Western reactions, he no longer does. His continuing denials of Russian involvement are a mocking ritual, a sign of unwillingness to negotiate rather than a nod to international pressure.

"All these sanctions were like poultices for a dead man," a distraught Yatsenyuk said today. "They did not help." He called for the West to freeze Russia's assets and financial transactions to force it to withdraw. The West, however, is unlikely to go that far. The sanctions have already contributed to economic contraction in Germany, and Europe cannot afford much more pain. Military aid is not an option: There is no country in the world where voters would back a war with Russia.

The Western world will probably wiggle out of its moral dilemma by blaming Poroshenko for being deaf to Russia's legitimate concerns about preserving Ukraine's status as a buffer state. No matter how unfair that sounds, Ukraine is now faced with the necessity of making concessions to Putin. It will take some time to sink in, but help of the kind Kiev really needs is probably not coming. Unless Poroshenko finds it in himself to bargain, eastern Ukraine may well end up a Russian-controlled no man's land like Abkhazia, South Ossetia and Transnistria. There is no face-saving solution for anyone anymore.