A man who says he posted a video on the Internet showing the brutal execution of two men from Central Asia and the Caucasus has turned himself in, a police official said Wednesday.

The man, in his early 20s, turned himself in Tuesday in Maikop, the capital of Adygei, a republic in southern Russia, the official said. Police have searched his home and seized his computer but have no firm evidence he was responsible for posting the video, the official said.

The video, which appeared Sunday on ultranationalist Web sites, shows two men kneeling in the woods with their mouths taped and their arms and legs tied up.

"We were arrested by Russian national socialists," they say in barely audible voices.

A subtitle on the video identifies the two as "colonists from Tajikistan and Dagestan." A Nazi flag stands in the background while two men in masks and camouflaged clothing give Nazi salutes.

Then, a man beheads one of the abducted men. Later a man is shown being shot in the head.

There was no way to independently confirm the content of the video. Russian prosecutors said they have opened a criminal investigation into its content.

An unknown organization called the National Socialist Party of Russia took credit for the video, which appeared on the site of another obscure group called National Socialism/White Power and in blogs on LiveJournal. By Monday evening, the video had been taken off some of the sites.

Alexander Verkhovsky, an activist with the SOVA center, which monitors hate crimes in Russia, said he had seen many videos in his work, but most of those that purported to depict murders appeared to have been staged or fake. This one appeared very genuine, he said.

"I've never seen anything that blatant," he said.

The man who turned himself in told police said he had received the video by e-mail from an unknown sender and had posted it on the Internet, the police official said, speaking on condition of anonymity in line with common practice. He said the man, who has a Russian last name, told police he was involved in the formation of a nationalist group in Adygei and had met with members of a movement called the Adygei Union of Slavs.

Police were investigating his claims, the official said.

Russia has seen a marked rise in xenophobia and racism in recent years, with numerous attacks on foreigners — many of them from the former Soviet republics in Central Asia and the Caucasus.