Bulgarian President Rosen Plevneliev denounced Russia's Vladimir Putin as an aggressive leader with a 19th-century empire-building style, in comments to be published Saturday.

"Russia is a nationalistic and aggressive state," Plevneliev told Germany's Frankfurter Allgemeine Zeitung.

"In President Putin's world, it is still the 19th century when there were the great powers and then their smaller neighbors which had to submit," he said.

Plevneliev, who holds an honorific post with diplomatic duties, said that Bulgaria's former Soviet master Russia "needs to learn to have partners, not vassals and subjects."

Many former communist states once under Moscow's control have criticized Russia for its role in the Ukraine conflict, accusing it of supporting rebels fighting for independence in the east.

Voters in Bulgaria are expected to return right-wing former premier Boyko Borisov to power a year and a half after he was forced to resign amid mass protests over corruption and economic stagnation in the European Union's poorest member state.