A three-minute video posted on several ultranationalist web sites recently is sickening. Two frightened young men, bound and gagged, are seen kneeling beneath a Nazi flag in a forest. "We were arrested by Russian national socialists," the men mumble through their gags. A caption identifies them as "colonists from Tajikistan and Dagestan."

One of the captors slices off a hostage's head with what appears to be a large knife. The other hostage is shot in the head, and he falls into a shallow grave.

The video credits a previously unknown group, the Russian National Socialist Party, for the executions.

While the killings have not been confirmed, several human rights activists and video experts say the recording looks genuine.

The video is a worrisome development that makes ultranationalists increasingly resemble Islamist extremists from the North Caucasus. The extremists have beheaded captives in the past, including federal soldiers and four foreigners working for a British telecommunications company in Chechnya in 1998.

The similarities don't stop there. Islamist extremists have staged a series of terrorist attacks, including train bombings, while two ultranationalists were convicted earlier this year of bombing a Grozny-Moscow train in 2005. Investigators said Wednesday that ultranationalists were most likely behind a bomb that derailed a train traveling from Moscow to St. Petersburg on Monday.

A group of ultranationalists are currently on trial for an attempt to kill Unified Energy Systems chief Anatoly Chubais with a roadside bomb in 2005.

Ultranationalists have grown increasingly bold about their cause in recent years, organizing bellicose anti-immigrant demonstrations that local authorities have readily authorized, citing the right to assembly and free speech. Interestingly, the same authorities have just as readily refused to sanction rallies by gay rights groups and The Other Russia opposition coalition.

While free speech is a right that deserves protection, violence in any form is unacceptable. This year alone, dozens of dark-skinned people have been beaten in attacks blamed on ultranationalists.

President Vladimir Putin and other officials have repeatedly condemned racially motivated hate crimes, and anti-extremism legislation passed by parliament in 2002 ostensibly aimed to stop the violence by toughening penalties for offenders. But police and prosecutors still regularly downplay attacks by classifying them as mere hooliganism, and the anti-extremism law seems to have been used more as a tool to fight opposition political groups.

The execution video should serve as a wake-up call for the Kremlin and law enforcement to send a clear message to ultranationalists that violence will not be tolerated. Complacency now would raise the risk that the attacks will not only continue but grow increasingly brutal -- threatening the very foundation of the multi-ethnic state.