DONETSK, Ukraine - With Ukrainian flags flying high and garlands of flowers in their hair, protesters marched through the heart of this city at sundown Monday.

"East and West together," they chanted.

But in Ukraine, even such anodyne appeals to unity can be a magnet for trouble. The protesters, including old men and grade-school-age children, were walking into a trap.

The club- and whip-wielding separatists who set upon these demonstrators were just the latest proof of the disarray that has engulfed eastern Ukraine. The attack marked a fitting coda to a day that also featured an assassination attempt on the mayor of the country's second-largest city and the fall of yet another government building to pro-Russia militants.

For the residents of this normally tranquil regional capital of one million people, it has been a shocking and sudden descent into lawlessness at the hands of shadowy forces that make their views known, but rarely their identities.

The men who attacked the pro-Kiev rally Monday evening wore black masks and wielded clubs while announcing their allegiance to Russia.

"They shouted, 'If you don't throw away your flags, we'll kill you. This place is Russia, not yours,' " said Olga Styagunova, 43, a marcher who ducked into a bakery to escape attack.

The fate of Kharkiv's mayor, who was shot in the back while out exercising, suggested that the separatists make good on their threats.

Gennady Kernes, known as a flamboyant character, was once a staunch supporter of Ukraine's pro-Russian President Viktor Yanukovych.

But after Yanukovych was ousted in February, Kernes swiveled his allegiance and forged civil relations with the new pro-Western government in Kiev. His eastern city was a hot spot for pro-Russian activists, but in recent weeks Kernes and police forces managed to retake government buildings occupied by separatists.

As of late Monday, the mayor was in critical condition, and officials said he was "fighting for his life."