Pro-Russian authorities in eastern Ukraine presented identity documents, maps and a business card to support their view that Ukrainian far-right nationalists had carried out a deadly attack in the eastern city of Slovyansk.
The nationalists and authorities in Kiev said it was a staged display to conceal the hand of Russian secret services in the gunfight, in which at least three people were killed.
The truth, as in so much of the standoff over Ukraine between Moscow and Kiev, was hard to establish.
A separatist fighter, who gave his name as Vladimir, said Right Sector members drove up to the checkpoint outside Slovyansk at around 2 a.m. "One of our men approached them. They shot him in the head and he fell immediately. There was some sniper fire. We had three dead and four wounded."
He said the separatists brought in reinforcements and in subsequent shooting two of the attackers were killed.
Local authorities later showed personal identity cards of people alleged to belong to Right Sector, a night-sight for a rifle, some maps and the business card of Dmytro Yarosh, the group's leader.
A Right Sector spokesman in Kiev poured scorn on the display. "They say that visiting cards of Dmytro Yarosh were found. It's surprising that Right Sector members carry around his visiting cards and they don't get destroyed when the car burns up," Artem Skoropadsky told Reuters.
It was the first time members of Right Sector, which was at the forefront of pro-Western demonstrations in Kiev, have been accused of involvement in any deadly violence in the east, where Russia has repeatedly said it fears civil war.
A spokesman for the group denied any role.
Russia's foreign ministry issued a statement backing the separatists' version of events and blaming armed members of Right Sector, an ultra-nationalist group which played a key role in the overthrow of Moscow-backed president Viktor Yanukovich in February.
It was a source of surprise, the ministry said, that the incident had happened after Russia, the European Union, the United States and Ukraine had signed the April 17 accord in Geneva calling on people to desist from using violence or intimidation.
In Kiev, Right Sector denied any involvement and blamed Russia's special forces, whom the Kiev leadership suspects of being behind separatist rebellion in the east, of organizing the attack.
Ukraine's state security agency, the SBU, also denounced what it called a "cynical" provocation by criminals and agents "who are supported and armed by Russian military intelligence".
And Kiev's interior ministry caustically commented on the speed "with which camera crews from Russian TV stations appeared at the scene of the shooting."
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