A pro-Russian separatist commander is alleged to have admitted killing 15 Ukrainian prisoners of war, as human rights activists urge an investigation into alleged war crimes by pro-Russian fighters.
Arseny Pavlov, who is also known as Motorola, is reported to have made the comments to the Kyiv Post in a phone interview.
Pavlov has been accused of shooting dead Ukrainian soldier Ihor Branovytsky, who was captured by separatists after taking part in the defence of the airport in Donetsk in January.
During the interview a man identified as Pavlov says he has killed 15 captured Ukrainian soldiers, but declines to comment on the death of Branovytsky.
He said: "I've shot 15 prisoners. I don't give a s**t. No comment. I kill whoever I want."
The Independent could not verify the voice was that of Pavlov.
The separatist commander also declined to comment when contacted by news agency Reuters.
Human rights group Amnesty International has said at least four Ukrainian soldiers have been shot dead in "execution-style" killings carried out by pro-Russian separatists earlier this year.
The organisation has described the torture and killing of prisoners as a war crime and urged a full investigation into the soldiers' deaths in eastern Ukraine.
Eduard Basurin, spokesman for the rebel forces, has denied all accusations of wrongdoing.
He told Reuters: "They don't have the facts. Let them present the facts, photographs, video, then we can comment. Otherwise this simply destabilises the situation."
Amnesty has said it has seen videos of at least four soldiers, who later died, held captive in January and February.
Ukraine crisis: A timeline of the conflict
Ukraine crisis: A timeline of the conflict
1/22 30 November 2013
Public support grows for the “Euromaidan” anti-government protesters in Kiev demonstrating against Yanukovych’s refusal to sign the EU Association Agreement as images of them injured by police crackdown spread.
2/22 20 February 2014
Kiev sees its worst day of violence for almost 70 years as at least 88 people are killed in 48 hours, with uniformed snipers shooting at protesters from rooftops.
3/22 22 February 2014
Yanukovych flees the country after protest leaders and politicians agree to form a new government and hold elections. The imprisoned former Prime Minister, Yulia Tymoshenko, is freed from prison and protesters take control of Presidential administration buildings, including Mr Yanukovych's residence.
Genya Savilov/AFP/Getty Imageses
4/22 27 February 2014
Pro-Russian militias seize government buildings in Crimea and the new Ukrainian government vows to prevent the country breaking up as the Crimean Parliament sets a referendum on secession from Ukraine in May.
Sean Gallup/Getty Images
5/22 16 March 2014
Crimea votes overwhelmingly to secede from Ukraine and join Russia in a ballot condemned by the US and Europe as illegal. Russian troops had moved into the peninsula weeks before after pro-Russian separatists occupied buildings.
6/22 6 April 2014
Pro-Russian rebels seize government buildings in the eastern cities of Donetsk, Luhansk and Kharkiv, calling for a referendum on independence and claiming independent republic. Ukraine authorities regain control of Kharkiv buildings on 8 April after launching an “anti-terror operation” but the rest remain out of their control.
7/22 7 June 2014
Petro Poroshenko is sworn in as Ukraine's president, calling on separatists to lay down their arms and end the fighting and later orders the creation of humanitarian corridors, since violated, to allow civilians to flee war zones.
8/22 27 June 2014
The EU signs an association agreement with Ukraine, along with Georgia and Moldova, eight months after protests over the abandonment of the deal sparked the crisis.
LOUISA GOULIAMAKI/AFP/Getty Images
9/22 17 July 2014
Malaysian Airlines flight MH17 is shot down over eastern Ukraine, killing all 298 people on board. Ukrainian intelligence officials claim it was hit by rebels using a Buk surface-to-air launcher in an apparent accident.
10/22 22 August 2014
A Russian aid convoy of more than 100 lorries enters eastern Ukraine and makes drop in rebel-controlled Luhansk without Government permission, sparking allegations of a “direct violation of international law”.
11/22 29 August 2014
Nato releases satellite images appearing to show Russian soldiers, artillery and armoured vehicles engaged in military operations in eastern Ukraine.
12/22 8 September 2014
Russia warns that it could block flights through its airspace if the EU goes ahead with new sanctions over the ongoing crisis and conflict
13/22 17 September 2014
Despite the cease-fire and a law passed by the Ukrainian parliament on Tuesday granting greater autonomy to rebel-held parts of the east, civilian casualties continued to rise, adding to the estimated 3,000 people killed
14/22 16 November 2014
The fragile ceasefire gives way to an increased wave of military activity as artillery fire continues to rock the eastern Ukraine's pro-Russian rebel bastion of Donetsk
15/22 26 December 2014
A new round of ceasefire talks, scheduled on neutral ground in the Belariusian capital Minsk, are called off
16/22 12 January 2015
Soldiers in Debaltseve were forced to prepare heavy defences around the city; despite a brief respite to the fighting in eastern Ukraine, hostilities in Donetsk resumed at a level not seen since September 2014
17/22 21 January 2015
13 people are killed during shelling of bus in the rebel-held city of Donetsk
18/22 24 January 2015
Ten people were killed after pro-Russian separatists bombarded the east Ukrainian port city of Mariupol
19/22 2 February 2015
There was a dangerous shift in tempo as rebels bolstered troop numbers against government forces
20/22 11 February 2015
European leaders meet in Minsk and agree on a ceasefire in eastern Ukraine beginning on February 14. From left to right: Belarus President Alexander Lukashenko, Russian President Vladimir Putin, German Chancellor Angela Merkel, France's President Francois Hollande and Ukrainian President Petro Poroshenko.
MAXIM MALINOVSKY | AFP | Getty Images
21/22 13 February 2015
Pro-Russian rebels in the city of Gorlivka, in the Donetsk region, fire missiles at Ukrainian forces in Debaltseve. Fighting continued in Debaltseve for a number of days after the Minsk ceasefire began.
ANDREY BORODULIN | AFP | Getty Images
22/22 18 February 2015
Ukrainian soldiers repair the bullet-shattered windshield of their truck as their withdraw from the strategic town of Debaltseve. Following intense shelling from pro-Russian rebels, Ukrainian forces began to leave the town in the early hours of February 18.
Brendan Hoffman | Getty Images
Their bodies were later photographed in a morgue, it has been reported.
Amnesty said: "There are signs of bullet wounds to their heads and upper parts of their bodies."
The human rights group said it has also seen a video of Branovytsky.
Denis Krivosheev, the deputy director for Amnesty in Europe and Central Asia, said in a statement: "The torture, ill-treatment and killing of captured, surrendered or wounded soldiers are war crimes."
Mr Krivosheev also called for an investigation and for those responsible to be brought to fair trail.
In Kiev, a comrade of Branovytsky said he witnessed his killing.
Yury Shkabura, 42, told Reuters television he heard a doctor tell Pavlov that Branovytsky needed medical attention at hospital.
He said: "Five minutes later, Motorola came back and shot him twice. He stepped back and said: 'I have already cured him'."
A medical certificate produced by the soldier's mother has stated he died from two bullet wounds in his head.
Ukrainian State Security official Vasil Vovk has said Kiev authorities want Pavlov on an international wanted list.
He said: "This person will bear responsibility for crimes against humanity, torture, murder of Ukrainian citizens including servicemen of the Ukrainian armed forces."
More than 6,000 people have been killed since fighting broke out last year between pro-Russian separatists and Ukrainian forces.
A ceasefire was brokered two months ago, although both sides have accused each other of intensifying attacks in eastern terrorities.
Additional reporting by ReutersReuse content