Russian authorities on October 13 prevented the sister of Ukrainian pilot Nadia Savchenko from testifying in her defense in her controversial murder trial.
Savchenko's sister Vira was meant to appear this week as the main witness for the defense against charges of murdering two Russian reporters, which could bring a 20-year jail term for the Ukrainian servicewoman.
The case has been condemned as a miscarriage of justice by human rights groups.
Vira Savchenko wrote on Facebook that Russian authorities told her at the border that she had been banned from entering the country until 2020, by orders of the Russian Federal Security Service.
A spokesman for the FSB in Moscow refused to comment.
The 34-year-old helicopter pilot has denied accusations that she helped direct an artillery strike that killed two Russian state television reporters in eastern Ukraine in June 2014.
Her lawyer Mark Feigin tweeted that "Nadia Savchenko has now been deprived of her right to a defense." He vowed to appeal the FSB decision.