A Belarusian court in December sentenced Dmitry Konovalov and Vladislav Kovalyova to death for an April bombing of a subway in Minsk that killed 15 people and left 200 injured.
Thorbjorn Jagland, secretary-general for the European Council, expressed frustration with President Alexander Lukashenko's refusal to overturn the death sentence.
Jagland said the European Council believes death is not the same as justice.
"I reiterate my call to the authorities in Belarus to put an immediate end to the use of capital punishment," he was quoted by Russia's state-run news agency RIA Novosti as saying.
Lukashenko, the only president an independent Belarus has had, allegedly said before the court delivered its verdict that the accused should receive "the strictest punishment."
Minsk has been criticized for political repression. The Belarusian Association of Journalists said this week that three of its members were, without explanation, prohibited by the government from leaving the country.
Belarus is the only European country that has a death penalty.