State media in Belarus say the two men convicted of carrying out a 2011 subway bombing attack in Minsk that left 15 dead and hundreds wounded have been executed.
In a brief report, state news agency BeITA said Uladzislau Kavalyou and Dzmitry Kanavalau were put to death.
The judicial killings came just days after President Alyaksandr Lukashenka refused a plea for clemency on behalf of the two factory workers.
They also came despite appeals from foreign governments and the European Union to spare the two mens' lives until "considerable doubts and questions" in the case, in the words of a spoeksman for German Chancellor Angela Merkel, could be dispelled.
Human rights activist Lyudmila Gryaznova condemned the executions, saying: "The execution of the so-called terrorists, whose guilt remains under suspicion, gives the appearance that the government is concealing the traces of the crime."
AP news agency reported that people angered by the executions lit candles outside the Minsk subway station and outside the Belarusian Embassy in Moscow on March 18.
They were killed with a single bullet to the back of the head, as prescribed under Belarusian law.
The mother of Kavalyou, Lyubou Kavalyova, initially told Russia's RIA Novosti news agency she had received official notification about the execution of her son.
Kavalyova said she received a letter informing the family of the execution (see below for the letter, in Russian).
"My mother just took the notice out of the mailbox. The Supreme Court...a letter from March 16...that the order was carried out.... Mama received it, they killed him. Everything was in vain. Everything was in vain," a sobbing Tatsyana Kavalyova, Kavalyou's sister, told RFE/RL's Belarus Service.
Tatsyana Kavalyova Reacts To The Letter (in Belarusian)
The news comes after Lyubou Kavalyova told RFE/RL on March 16 that she had asked Belarus's president to stay the execution for at least one year, until her son receives a response to his appeal to the United Nations Committee on Human Rights over the death sentence.
Kavalyova later told Reuters her son's execution was revenge by Lukashenka's government.
"It all led to this," Kavalyova said. "They thought they could threaten the boys and the boys would keep it quiet. Yes, Dima [Dzmitry Kanavalau] kept it quiet, but my son did not.... They thought they would scare the children and they will be quiet. All their scenario of the investigation and of the court.... They would have executed him back then [in November 2011], but my son did not let them do it. So they got their revenge, against my son and against me."
In Brussels, Maja Kocijancic, the spokeswoman of EU foreign-policy chief Catherine Ashton, reacted to the news by saying, "if this is indeed confirmed, we condemn this."
"I can also add that of course we are aware of the terrible crimes that Mr. Kavalyou and Mr. Kanavalau were condemned for, and our thoughts are with the victims and the families," Kocijancic said, "but at the same time we also know that the two accused were not accorded due process including the right to defend themselves."
Ashton had appealed to Belarus on March 16 not to execute the two men condemned to death
on charges related to the bombing on the Minsk subway in April 2011.
A statement from Ashton's office said she was "very concerned" about the decision not to pardon Kavalyou and Kanavalau, who were sentenced in November.
Germany also urged Belarus on March 16 not to execute the two men, warning the executions could further strain relations between the two countries.
German Chancellor Angela Merkel's spokesman, Steffen Seibert, told journalists that Lukashenka's rejection of the execution appeal on March 14 filled Berlin with "great concern" that the sentences would imminently be carried out.
Seibert added there were "quite considerable doubts and questions" regarding the case against both men.
On March 14, Lukashenka had refused to grant clemency
to the two 26-year-old factory workers, despite the pleas of Kavalyou's mother
The quick investigation and lack of motives presented during the trial of the two men has sparked accusations that the bombing was a plot by security services to justify a crackdown against Lukashenka's political foes.
Lukashenka, who was reelected in a controversial December 2010 vote, has said that the blast was an attempt to destabilize the country by unknown enemies of the state. Belarusian investigators said the men were driven by "hatred for humankind," not political or religious motives.
On March 16, Belarusian activists held a ceremony to commemorate the subway explosion victims in Minsk to try to draw public attention to the situation faced by the two convicts.
The event was organized via social networks, where activists wrote that they wanted a new trial for Kanavalau and Kavalyou and a moratorium on the death penalty in Belarus.
Belarus is the last country in Europe to carry out executions.
With AP, ITAR-TASS, Reuters and AFP reporting
The letter received by Lyubou Kavalyova: