Amnesty International says "shocking new evidence" shows pro-Russian militants in eastern Ukraine have killed soldiers in their captivity execution-style.

RFE/RL's Claire Bigg spoke to Denis Krivosheyev, Amnesty International's deputy director for Europe and Central Asia.

RFE/RL: Amnesty International says it has evidence that the rebels killed four captive Ukrainian soldiers and talks about "execution-style killings." Please tell us more about this new evidence.

Denis Krivosheyev: We have seen a video of these four individuals in captivity -- they were taken captive following military action in January – where they are alive and in the custody of separatist forces. Then we have seen photo evidence of them dead. The cause of death is very clear from these photos: they were shot.

RFE/RL: What does Amnesty International know about these soldiers? Have they all been identified?

Krivosheyev: One of them was named publicly, Ihor Branovytskiy, his funeral took place in Kyiv a couple of days ago. The other three have not been named. We need to be cautious about protecting our sources, so I'm not ready to name them yet.

RFE/RL: If confirmed, do these killings amount to war crimes?

Krivosheyev: Anyone being ill-treated or killed in custody constitutes a war crime. Those responsible for this should be identified and prosecuted.

RFE/RL: In your opinion, is the apparent execution of these soldiers an isolated incident, or does this case highlight a broader trend?

Krivosheyev: There's quite a lot of evidence of ill-treatment and torture in custody, so I would be ready to call this a widespread practice. And I must emphasize that we have evidence of this happening on both sides. With regard to executions, only isolated cases reach us, so I'm not ready to state they are a mass phenomenon. But I do suspect very strongly that a lot more is happening than we know about.

RFE/RL: Amnesty International has called on Kyiv to investigate these deaths. But can the Ukrainian authorities realistically conduct a probe in a territory controlled by armed separatists?

Krivosheyev: Realistically, on their own, what they can do is very limited. What they must do is institute an impartial and independent investigation, which in Ukraine has always been a bit of a problem. But once they can assure that the investigation of this incident can be impartial, then I think it would come to the point where pressure from the international community would be required to enable Ukrainian investigators to access the territory where this happened, to have access to evidence and witnesses, and to do their work properly.