KIEV, Ukraine — Pro-Russian separatists who seized a provincial administration building in the eastern Ukrainian city of Donetsk proclaimed the region independent Monday — an echo of events prior to Russia’s annexation of Crimea. Ukrainian authorities called the move an attempt by Russia to sow unrest.

The Interfax news agency said the activists demanded that a referendum be held no later than May 11 on the possible secession of the Donetsk region, which borders Russia.

Outside the administration building, a barricade of car tires and razor wire was built up to keep police from retaking it. Police said those inside the building were armed.

Speaking in a televised address, acting President Oleksandr Turchinov called the events gripping eastern regions — where pro-Russian activists seized government buildings in at least three cities Sunday — an operation undertaken by Russia to sow instability.

“Anti-terrorism measures will be adopted against those that took up weapons,” Turchinov said, adding that parliament would convene Tuesday to consider tougher penalties for separatist actions and even ban parties that engage in separatism.

In a video posted on the Internet, an unidentified pro-Russia activist in the Donetsk government headquarters asked Russian President Vladimir Putin to send “peacekeeping troops” to the region.

“Without your support, without the support of Russia, it will be hard for us to resist the Kiev junta on our own,” he said, referring to the interim authorities that took power after the overthrow of Moscow-backed President Viktor Yanukovych in February.

Earlier in the day, Ukrainian Prime Minister Arseniy Yatsenyuk also accused Russia of being behind the unrest that broke out in the country’s eastern provinces Sunday and of seeking to sow instability as a pretext for sending troops across the border.