Vira Savchenko, the sister of Ukrainian parliamentarian Nadiia Savchenko, who is suspected of plotting a coup in Ukraine, has said that Ukrainian Security Service (SBU) officers questioned her on Thursday as part of a criminal investigation which was opened in 2015 and mentions Nadiia.

"I and Nadiia Savchenko's aide Tetiana Protorchenko were summoned as witnesses. The questions... that were asked are not new. All of the questions that came from the prosecutor general are linked with the case that was opened in 2015. This case existed in Ukraine when Nadiia was in captivity," Vira Savchenko told the ZIK TV channel on Thursday.

When asked what the mentioned criminal case centers on, Vira said that "the preamble to Nadiia's indictment says that she is accused of feeling discontent about the socioeconomic situation... and is accused of preparing a coup and an assassination attempt on the president."

"It is not totally clear to me what [Nadiia is suspected of] exactly and why this case was opened in 2015. It is a mystery on which I hope the lawyers will shed light. But the lawyers do not have all of the case materials. That is why we are waiting now," she said.

It was reported that on March 22, the Ukrainian Verkhovna Rada granted the prosecutor general's recommendation and gave its consent to prosecute, detain, and arrest Savchenko.

Savchenko is suspected of preparations to violently change or dismantle the constitutional system or for the seizure of power, preparations for assassinating a statesperson or a public figure, preparations for a terrorist attack, the establishment of a terrorist group or a terrorist organization, and the illegal handling of weapons, ammunition, or explosives.

Kyiv's Shevchenkivsky District Court ruled on March 23 to place Savchenko under arrest pending trial for 59 days, until May 20. Savchenko announced a hunger strike on the same day.

On March 29, the Kyiv Appeals Court turned down an appeal lodged by Savchenko's defense team contesting the Shevchenkivsky District Court's ruling on taking her into pretrial custody.

Savchenko underwent a forensic psychological evaluation and a lie detector test on April 17.