MOSCOW - A leading Chechen rebel on Wednesday called on Islamist militants in Russia's North Caucasus to disrupt the upcoming Olympics in the Black Sea resort of Sochi, reversing his previous appeal not to target civilians in the region.

Sochi is hosting the Winter Games in February, a pet project for President Vladimir Putin, who is determined for them to be a success. The overall bill for the games stands at $51 billion, making them by far the most expensive Olympics in history.

Doku Umarov, a widely known Chechen rebel leader, urged his fighters to "do their utmost to derail" the games, which he described as "satanic dances on the bones of our ancestors."

"We have the obligation to use all means to prevent this," he said in a video posted on a rebel website on Wednesday.

Umarov last year urged his fighters to avoid hitting civilian targets because Russians in Moscow were taking to the streets en masse to protest against Putin.

Security experts have said the Islamic insurgency raging across the North Caucasus mountains that tower over Sochi is a daunting threat to the games — although rebels have not attacked Sochi so far.

Dagestan, which lies about 500 kilometres (300 miles) east of Sochi, has become the centre of the insurgency that spread across the North Caucasus region after two separatist wars in the 1990s in neighbouring Chechnya. Rebels seeking to carve out a caliphate, or Islamic state, have targeted police and other officials in near-daily shootings and bombings. Umarov is believed to be their most influential leader.

Tamerlan Tsarnaev, the elder of the two ethnic Chechen brothers who are accused of staging the Boston Marathon bombings, spent six months last year in Dagestan.

Jean-Claude Killy, head of the IOC co-ordination commission for Sochi, said such threats are to be expected.

"We get threats before every Olympics," he told The Associated Press. "This cannot be taken lightly. I think the Russians are well equipped to face the challenge."

The Sochi 2014 Organizing Committee said in an emailed comment that ensuring security at the games is "the responsibility of the state" and will be its priority.

"We are confident that the games will be safe and comfortable for all as guaranteed by the Russian state," the committee said.

Russia's National Anti-Terrorism Committee said in a statement on Wednesday that it is working to eliminate threats at all international sporting events in the country including the Olympics. Officials said that they aim "to identify and avert various threats, including those of terrorism."

Ramzan Kadyrov, a strongman who rules Chechnya, played down the influence of Umarov and promised that his security forces would track him down. "Before the Olympics, I think, I'm sure, that we will destroy him," Kadyrov told the Interfax news agency. "We search for him every day, but he is nowhere to be found."

Press officers for the Interior Ministry in Russia's southern district, which includes the North Caucasus, declined to comment.

An officer of the Interior Ministry's special task force in the North Caucasus, who asked not to be identified because he was not allowed to comment publicly, told The Associated Press that Umarov's statement could prompt Russians to step up their efforts to comb the mountainous areas where Umarov could be hiding.

The United States declared Umarov's group a terrorist organization in 2011 and offered up to $5 million for information leading to his capture.

Umarov's group is blamed for bombing a Moscow airport in January 2011, two subway stations in 2010 and a Russian train in 2009.

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AP writer Stephen Wilson in Lausanne, Switzerland, and Sergei Venyavsky in Rostov-on-Don, Russia, contributed to this report.

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  • Olympic rings for the 2014 Winter Olympics are installed in the Black Sea resort of Sochi, southern Russia, late Tuesday, Sept. 25, 2012. With the Winter Olympics a year away, IOC President Jacques Rogge praised Sochi organizers on Wednesday, Feb. 6 and defended the $51 billion price tag.

  • In this Friday, April 5 photo ski resort employees scale down a pile of snow which is being covered by insulated fabric. The Rosa Khutor Alpine skiing resort which is hosting the 2014 Winter Olympics is set to store nearly half a million cu. meters of snow collected in piles and tightly covered with insulated blankets.

  • Activists of ultranationalist organizations rally in Moscow, on May 1, to call for President Vladimir Putin's resignation and a boycott of the 2014 Winter Olympic Games in Sochi.

  • In this Friday, April 5 photo a ski resort employee stands on top of a snow storage next to rolls of insulated blankets. The Rosa Khutor Alpine skiing resort which is hosting the 2014 Winter Olympics is set to store nearly half a million cu. meters of snow collected in piles tightly covered by insulated blankets.

  • In this photo dated Monday, Feb. 4, an aerial view of the Olympic Park as construction works continue in the lead up to the upcoming winter games in Sochi, Russia. With just one year till the opening ceremony of the winter Olympic 2014 Sochi Games, the Black Sea resort of Sochi is a vast construction site sprawling for nearly 40 kilometers (25 miles) along the coast and 50 kilometers (30 miles) up into the mountains, with no escape from the clang and clatter of the construction works, the drilling, jack-hammering and mixing of cement.

  • In this photo dated Feb. 2, the Iceberg skating arena at the Russian Black Sea resort of Sochi,

  • In this photo dated Monday, Feb. 4, an aerial view of the Olympic Park as construction works continue in the lead up to the upcoming winter games in Sochi, Russia.

  • Activists from Reporters Without Borders stands in front a banner with blood-covered brass knuckles in the form of the Olympic rings which are displayed on the fences of the Russian embassy in Paris, Friday, March 1. Reporters Without Borders activists protest against the 2014 Sochi Winter Olympics games in Russia and the working conditions against journalists working in Russia.

  • A Half-pipe is seen during of the FIS World Cup snowboarding half-pipe event, in Rosa Khutor ski resort, some 60 km east of Sochi, Russia, Thursday, Feb. 14. The Roas Khutor resort forms part of the venue which will host the Sochi 2014 Winter Olympics.

  • Russian President Vladimir Putin and IOC President Jaques Rogge, bottom left and second left, press a symbolic button to mark one year to the start of 2014 Winter Olympics, in Sochi, Russia, Thursday, Feb. 7.

  • Russian President Vladimir Putin, left, and IOC President Jaques Rogge shake hands after pressing a symbolic button to mark a 1 year to the start of 2014 Winter Olympics, in Sochi, Russia, Thursday, Feb. 7.

  • Fireworks are seen over the Bolshoi Ice Dome stadium during a ceremony to mark a one year to the start of 2014 Winter Olympics, in Sochi, Russia, Thursday, Feb. 7.

  • The shadow of a performer is cast on a board as spectators watch a ceremony to mark the one year to the start of 2014 Winter Olympics, in Sochi, Russia, Thursday, Feb. 7. Russia on Thursday marked the one-year countdown to the Sochi Games, which are considered a matter of national pride and a priority for President Putin. The countdown celebrations culminated later Thursday in a star-studded ice show at one of the Olympic arenas, attended by Putin and IOC President Jacques Rogge.

  • A countdown clock for the 2014 Sochi Olympics is installed outside the Kremlin in Manezh Square, with Kremlin's Spassky Tower at right in the background, in Moscow, Russia, Thursday, Feb. 7, 2013. (AP Photo/Mikhail Metzel)