How will Russia respond to Ukraine’s military show of force?

A quick scan of the headlines and you might safely assume that all is lost in eastern Ukraine.

The BBC's Sarah Rainsford says it was a critical time for Ukraine to act. For weeks, it looked as though the country had lost control over its eastern cities, as pro-Russian groups took over government buildings across the region.

"And now the Ukrainian government has decided to respond," she says. "The question is how far they are willing to go."

This is largest show of force from the Ukrainian military so far. Rainsford, who is based in eastern Ukraine, says Ukraine's army descended in helicopters and armored personnel carriers. It was a full military response to what the government in Kiev calls a terrorist takeover in parts of the country.

The pro-Russian militias responded to the attack by shooting down two helicopters using mobile rocket launchers. Rainsford says it proves the militiamen are well armed. Kiev believes the arms are coming from Moscow. But Rainsford says the BBC hasn't confirmed yet who is supplying the arms.

Moscow has condemned the show of force by Ukraine, calling it "criminal."

Vyacheslav Nikonov, a Russian MP with United Russia and a member of the Kremlin's foreign affairs committee, says Russia will not sit by if violence continues.

"It really would be very, very hard for Russia to stay silent in the case of a bloody civil war," he says.

And Nikonov doubted the Ukrainian military had the capacity to sustain a large-scale offensive.

In eastern Ukraine, Rainsford says most everyone is worried about a military response by Russia. Moscow has been looking for a pretext to intervene in the area and take over.

"Moscow has always said it believes it has the right to protect ethnic Russians in Eastern Ukraine," she says, "and that it would send in what it calls 'peace keepers' if it felt that was necessary."

Where will the conflict go from here? Rainsford says that's the million-dollar question. She says it depends on what the endgame is and it depends on how Kiev decides to play it.

The government is very concerned about causing casualties. Kiev is certainly aware it doesn't match up to Russia's military might. But Russia has to weigh the global reaction if it sends troops into Ukraine yet again.

The European Union and the United States have both made extremely strong comments in support of Kiev. The two global heavyweights also said the pressure is on Russia to de-escalate the conflict and stop it before it descends into all-out war.