SLOVYANSK, Ukraine — A column of armored vehicles flying Russian flags today drove into a Ukrainian city controlled by pro-Russia demonstrators, dampening the central government’s hopes to re-establish control over restive eastern Ukraine.

One of men aboard the vehicles said they were Ukrainian soldiers who had defected to the pro-Russian side. If that’s true, it raises the specter of an uprising by defected Ukrainian forces in eastern regions of the country. But a senior lawmaker denied any defections had taken place, instead insisting the men on the vehicles were Ukrainian soldiers conducting a false-flag operation to move about freely.

The six vehicles with troops in camouflage sitting atop entered the city of Slovyansk, a hotbed of unrest against Ukraine’s acting government. Insurgents in Slovyansk have seized the police headquarters and administration building, demanding broader autonomy for their eastern Ukraine region and closer ties with Russia.

Eastern Ukraine was the support base for Russia-friendly President Viktor Yanukovych, who was ousted in February after months of protests in the capital, Kiev, which were ignited by his decision to back away from closer relations with the European Union and turn toward Russia. Opponents of the government that replaced him alleged the new authorities will repress eastern Ukraine’s large Russian-speaking population.