The EU on Sunday said that Russia's President Vladimir Putin bore "ultimate responsibility" for the death of Alexei Navalny, as it paid tribute to the late opposition figurehead on the one-year anniversary of his passing.The European Union's foreign policy chief, Kaja Kallas, said Navalny "gave his life for a free and democratic Russia" and called for the release of all political prisoners in the country."Today marks one year since the death of Russian opposition leader politician Alexei Navalny, for which President Putin and the Russian authorities bear ultimate responsibility," Kallas said in a statement.The charismatic Navalny Putin's main opponent who campaigned against government corruption died a year ago while incarcerated in a remote Arctic penal colony.Russian authorities have never fully explained his death, which they said happened while he was walking in the prison yard."As Russia intensifies its illegal war of aggression against Ukraine, it also continues its internal repression, targeting those who stand for democracy," Kallas said.Navalny's lawyers remain "unjustly imprisoned, together with hundreds of political prisoners," she added."Russia must immediately and unconditionally release Alexei Navalny's lawyers and all political prisoners," Kallas said.Navalny Putin's main opponent was declared an "extremist" by Russian authorities, a ruling that remains in force despite his death, which came less than a month before a presidential election that extended Putin's more than two-decade rule.In Russia, anybody who mentions Navalny or his Anti-Corruption Foundation without stating that they have been declared "extremist" is subject to fines, or up to four years in prison for repeated offences.Until his death, the 47-year-old continued to call for Russians to oppose the Kremlin and denounced Moscow's Ukraine offensive, even from behind bars.