Russian Islamist militants have promised to deliver "a present" to President Vladimir Putin at the Sochi Olympic Games in a video which identifies them as suicide bombers killed in attacks last month.
Russia's President Vladimir Putin looks on during his interview to Russian and foreign journalists the Black Sea resort of Sochi, on January 19, 2014
In the video posted on well-known North Caucasus Islamist website VDagestan.com, two men sitting in front of a jihadist flag warn the Russian authorities of planned attacks in Sochi.
"As for your Olympics, something that you want so much, we also have a present for you," says one of the men, as the other smiles.
"And for those tourists who will come, inshallah, for these tourists there is also a present," one says, using the Arabic phrase for "God willing."
The video cast an ominous shadow over the Games which start on February 7 amid unprecedented security measures.
"There is a real threat for Sochi, and the desire to spoil the Games is also real," said analyst Pavel Felgenhauer. "We have no idea of their capabilities."
The introduction to the video said that the men were responsible for two suicide bombings in the southern city of Volgograd last month -- Russia's deadliest in three years -- which killed a total of 34 people.
The attacks struck a rail station and a trolleybus.
The video named the suicide bombers as Suleiman and Abdurakhman and said they carried out "the operation in Volgograd". The end of the video showed the explosion at the station and the charred carcass of the trolleybus.
The video also depicted what it described as "preparation for the operation", showing hands in red gloves assembling explosives and taping wires to a forearm.
It was released just before the Olympic torch relay arrived in Volgograd on Monday.
The website also published a Russian-language statement by a group calling itself Ansar al-Sunnah promising Russians it would "fill their houses with blood."
"Attacks such as those in Volgograd are only the beginning of your sufferings," said the statement signed by a group leader, "Umar."
It was not immediately clear whether the group is affiliated with the eponymous Sunni organisation that claimed credit for multiple attacks in Iraq in the 2000s.
Two blasts rocked Volgograd on December 29 and 30 when one suicide bomber detonated himself at the southern city's main railway station while the second hit a packed trolleybus.
Lifenews website last week published what it said was security footage of the bomber entering the train station, with the man's face obscured by sunglasses and a winter hat.
'They could have planted a bomb a year ago'
Some analysts said they doubted the affiliation of the Iraqi group with Dagestani militants in the video, who delivered their speech entirely in Russian.
Fears of attacks in Sochi were amplified by wanted posters around the Olympic city of purported female suicide bombers.
The posters seen by AFP correspondents show four women in headscarves, three of whom are from Dagestan and are described as "possibly preparing to become suicide bombers".
"All of this shows that the threat is very real," said Andrei Soldatov, who runs the website Agentura.Ru about the Russian security services.
Even the strictest security measures cannot prevent all attacks, added analyst Alexei Malashenko of Carnegie Moscow Center.
"They could have planted a bomb a year ago," he said. "You can't prevent everything."
Islamist insurgents based in North Caucasus republics such as Dagestan who are seeking their own independent state have vowed to disrupt the Sochi Games in order to undermine Putin's rule.
The United States this month issued a travel alert to citizens travelling to Sochi that "they should remain attentive regarding their personal security at all times."
US Congressman and chairman of the House Intelligence Committee Mike Rogers, speaking on CNN, expressed concern that Russia is not sharing all of the information with US intelligence needed "to protect our athletes in the Games."
"So what we're finding is they aren't giving us the full story about what are the threat streams, who do we need to worry about," the lawmaker said on Sunday.