Russia building a pretext to push deeper into Ukraine?

DONETSK, Ukraine -- The growing and increasingly violent demonstrations in Donetsk have claimed their first casualty, a 22-year-old man who was stabbed to death Thursday.

Hospital officials told CBS News two people were killed and more than a dozen more were wounded in the nighttime clashes.

The trouble began when two rival groups gathered in Lenin Square, one pro-Russian, the other, pro-Ukrainian. They were equal in number, with maybe several hundred on each side, one group flying Russian flags and shouting their support for Russian president Vladimir Putin, the other waving the Ukrainian flag and condemning the Russian military takeover of Crimea.

First they began hurling insults at each other, then eggs, bottles and fireworks.

A thin line of riot police separating the groups quickly collapsed and melted away.

When some pro-Ukrainian demonstrators tried to get away on a bus, pro-Russian protestors pelted it with rocks, smashing the windows. Somebody tossed a smoke bomb through one of the broken windows, causing everyone inside to flee in panic.

We've seen these demonstrations and counter demonstrations all week. This was by far the most violent, and the first that ended in death.

There is very good reason for grave concern in this city, not far from the Russian border, where demonstrators are demanding the same kind of referendum scheduled to be held this weekend in Crimea.

It's why former heavyweight boxer and presidential candidate Vitaly Klitschko came from Kiev on Sunday, in his words, to "unite the city and unite Ukraine."

Not even a six-foot-eight, 240-pound world champion boxer could face a thousand furious pro-Russian protesters. They had to call it off to avoid confrontation.

The violence here plays right into the hands of the Russians.

The bloodshed in Donetsk prompted the Russian Foreign Ministry to announce Friday that Moscow "reserves the right to take people under its protection."

In other words, to launch a military invasion of Donetsk under the pretext of "protecting Russians," just as it did in Crimea.

Many consider themselves ethnic Russians, and particularly older generations who hearken back to the days before the breakup of the Soviet Union.

They watch Russian television here, which is predominated by reports insisting the takedown of Kremlin-backed Ukrainian President Victor Yanukovich was the work of "fascists."

Many here believe it wholeheartedly, and they believe it when Russians stir fears that these "fascists" will take over here, too.

It doesn't help that Donetsk is Yanukovych's hometown.

Neither side is completely innocent in instigating trouble here, but the pro-Russian demonstrators have tended to be far more aggressive -- and the first to attack.

Pro-Ukrainian activists said the two who reportedly died in Thursday's clashes came from their side.

The Ukrainian government has tried to avoid the kind of confrontation that could provoke a Russian response, but tensions are rising here on the eve of the vote in Crimea this weekend.