Belarus has executed one of two convicted Minsk metro bombers, Vladislav Kovalyov, his sister told AFP Saturday, adding that he had been shot dead. Tatyana Kovalyova confirmed by telephone from the family's home town of Vitebsk in eastern Belarus that they had been informed of the execution of 26-year-old Kovalyov, who had pleaded not guilty to acting as an accomplice. "We will not stop. We will rehabilitate Vladislav. God forbid that this happen again, that they shoot an innocent person," she said. Vyasna rights group posted a scan on its website of the brief letter dated Friday to Kovalyov's mother from the Supreme Court saying that "the sentence of your son Vladislav Kovalyov has been carried into effect." The curt letter signed by the deputy chairman of the Supreme Court tells Lyubov Kovalyova that she can collect a death certificate but does not mention collecting her son's body. The blast in April 2011 struck the city's busiest metro station killing 15 people near the offices of strongman President Alexander Lukashenko, who has ruled the ex-Soviet state with an iron grip for nearly 18 years. Lukashenko on Wednesday refused to grant clemency to the two men, Kovalyov and Dmitry Konovalov, sentenced to death for the attack. European Union foreign policy chief Catherine Ashton on Friday had urged Belarus not to carry out the executions, calling for Minsk to enter a moratorium on the use of the death penalty. Kovalyov was sentenced as an accomplice while Konovalov was found guilty of bringing explosives to a central Minsk metro station and setting off the blast on a busy platform. Kovalyov, 26, had pleaded not guilty in court and retracted his initial confession, saying it had been made under pressure from investigators. No information was available on the fate of the second man Konovalov, who had pleaded guilty to the attack and never applied for amnesty. Kovalyov's sister Tatyana said that the family was not in contact with the other man's relatives and did not know whether he was still alive. The blast marked the worst attack in the republic's post-Soviet history and was immediately blamed by the authoritarian president on foreign and domestic enemies. The two suspects were also found guilty in connection with a bomb attack at Independence Day celebrations in Minsk in 2008 as well as several attacks in their native city of Vitebsk in 2005 that injured more than 100 people. Kovalyov's mother waged a tireless campaign for her son's life, travelling to Strasbourg to tell the Council of Europe Parliamentary Assembly that both young men had been framed. She also filed an appeal directly to Lukashenko for clemency and on Friday asked him to delay the execution for a year after she submitted a complaint to the United Nations Committee on Human Rights. "Our mother is very bad now. She can't speak," Kovalyov's sister Tatyana said. Lukashenko, who was re-elected in December 2010 in a controversial vote, has said that the blast was an attempt to destabilise the country by unknown enemies of the state. The speed of the investigation and lack of motive for the two factory workers to carry out the attack even sparked speculation that it was a plot by security services to justify a crackdown on Lukashenko's foes. The attack coincided with a massive government crackdown on the opposition who took to the streets to protest against Lukashenko's re-election. Belarus, which has grown increasingly isolated from the West, is the last country in Europe to administer the death penalty, although the practice is highly secretive and no official statistics exist. The country's former executioner wrote a book detailing the practice after fleeing to Germany, saying that prisoners are shot in the back of the head and their bodies buried in a secret location.