Amnesty International has claimed that it has proof that pro-Russian separatists in conflict-torn eastern Ukraine have summarily shot four Ukrainian soldiers, who were taken hostage earlier.
The monitoring group also said that one government soldier was shot at point blank range by a separatist commander, reported the BBC.
Amnesty alleged that it had videos showing three Ukrainian soldiers alive in captivity, then dead in a morgue with gunshot wounds to their heads and upper bodies. It added that the killings amounted to war crimes.
Denis Krivosheev, Europe and Central Asia Deputy Director at the organization, said that the claims must be "promptly, thoroughly and impartially" probed, and the perpetrators be brought to justice by recognized authorities.
A "fragile" ceasefire has been in place in the conflict-torn region since February.
Rights groups have accused both sides of committing atrocities.
At least 6,000 people have been killed since the conflict broke out last year.
