WASHINGTON – National security experts are expressing increasing alarm over the possibility Islamic militants could use a “dirty” bomb at the 2014 Winter Olympics in Sochi, Russia, and spark mass panic at the seaside location where potential escape routes could become choked.

Despite the 1,500 mile “ring of steel” that Russian President Vladimir Putin said surrounds Sochi to prevent the infiltration of North Caucasus militants, who have vowed to disrupt the Olympics with violence, experts say that a dirty bomb not only would be difficult to stop but could cause a major disruption.

A dirty bomb, known as a radiological dispersal device, or RDD, is a weapon combining radioactive material with conventional explosives. Essentially, it would have nuclear materials attached to something as simple as plastic explosives.

Experts say materials suitable to make a radiological weapon include nine reactor-produced isotopes such as americium-241, californium-252, cesium-137, cobalt-60, iridium-192, plutonium-238, polonium-210, radium-226 and strontium-90.

The “ring of steel” of some 50,000 Russian security personnel includes the Olympic village and the 30-mile road and rail transport to the mountain village where the Olympics will take place. Sources say that the mountainous road network wasn’t designed to handle large numbers of vehicles, making chokepoints along the way ideal for attacks.

In addition, the lack of interconnectedness of the 1,400 miles of roads will make detours and avenues of escape almost impossible.

There already have been three recent explosions by North Caucasus militants in the Russian city of Volgograd. The perpetrators posted a video before the attacks vowing there would be “surprises” at the Olympics.

In addition, an all-points bulletin has gone out for three “black widows,” or widows of dead militants. They are Jhannet Tskhaeva from Dagestan, Oksana Aslanova from Turkmenistan in Central Asia and Ruzana Ibragimova.

Further, there now are two men, identified as Ruslan Saufutdino and Murad Musaev, also being shown on wanted posters, which sources say suggests there may be holes in Sochi’s security. The concern is that the jihadists may already be within the “ring of steel.”

The threat of Islamic militant attacks has prompted a recent travel advisory by the U.S. State Department. The U.S. has placed military aircraft in Germany on alert and deployed two warships to the Black Sea to be on standby at the seaside city of Sochi.

Some countries such as Canada are considering whether even to allow their athletes to participate. Even the National Hockey League is considering keeping its athletes at home.

Rep. Mike McCaul, R-Texas, chairman of the House Homeland Security Committee, who recently returned from Sochi, said that the security threats “to this particular Olympics are the greatest I think I’ve ever seen.”

He said consideration should be given to canceling the Olympics.

However, he said that the U.S. team will be the largest and should not allow the terrorists “to win.”

The reason McCaul is concerned was underscored by a call by al-Qaida leader Ayman al-Zawahiri for a global jihad against the Olympics.

Zawahiri’s threat is only the latest from Islamic militants. Last week, the Sunni terrorist group Ansar al-Sunna released a video threatening attacks against the Olympics.

In addition, the leader of the North Caucasus militant fighters, Dokku Umarov, has issued a call for his Islamic militants to “do their utmost to derail” the “satanic” games.

Umarov, who has led the fighting for years against Moscow, wants to establish a Caucasus Emirates subject to strict Islamic law, or Shariah, in the North Caucasus region that includes the predominantly Muslim Russian provinces of Chechnya, Ingushetia, Dagestan, North Ossetia, Karachay-Cherkessia and Kabardino-Balkaria.

He wants to split the republics from the rest of Russia, which some ethnic Russians support. But Russian President Vladimir Putin sees such action as a potential slippery slope that would prompt other ethnic entities throughout Russia to also seek independence.

Umarov’s threat is the realization of Moscow’s worst fear, since it sees security at the games as one of its highest priorities. It is estimated that Moscow will spend more than $51 billion to make a success of the games, which it sees as a showpiece for its economic and technological achievements.

Umarov has vowed to us “all means” to disrupt the Olympics.

Security experts say “all means” could include the use of dirty bombs, which are conventional explosives laced with radiological materials.

“Several factors make a radiological attack attractive to terrorists,” according to a report of the open intelligence Langley Intelligence Group Network, or Lignet.

Preparation for a dirty bomb attack would be low, requiring only a small amount of a radiological source material and conventional explosives.

“The technical requirements also are low,” the report said. “No specialized training is required beyond knowing how to detonate an explosive.

“The havoc caused by a successful attack would be substantial for competitors and spectators alike,” the report warned. “The prospect of being involved in an attack involving radioactivity could lead easily to panic. The ensuing disruption would result in enormous financial losses and raise questions about where and how future games should be held.”

Underscoring the concern over the use of a dirty bomb is the assessment that the North Caucasus fighters have access to radioactive materials and the capability to make dirty bombs.

In November 1995, Chechens planted a cesium-filled explosive package in Moscow’s Ismailovsky Park to show they had an ability to construct a radiological bomb. The rebels alerted the press of the buried cache in the park, where authorities found a partially buried container.

To this day, the source of the cesium remains unknown.

Then, in December 1998, the head of the Russian-backed Chechen Security Service at the time, Ibragim Khultygov, announced that his security team had found a container filled with radioactive materials attached to an explosive mine hidden near a railway line.

The security team defused the bomb in a suburban area of Argun 10 miles east of the Chechen capital of Grozny, where a Chechen rebel group was known at the time to have an explosives workshop.

In September 1999, thieves attempted to seal a container holding some 200 grams of radioactive materials from the Radon Special Combine chemical factory in Grozny, Chechnya.

Following exposure to the container, however, one of the suspects died and the other collapsed, even though they held the container for only a few minutes while carrying it out of the factory.

In December 2001, three woodcutters found two heat-emanating containers near their campsite in the remote Muslim Caucasus region of Abkhazia, Georgia. They intended to use the containers as a heat source but within hours began to fall ill and later went to a hospital for treatment.

The International Atomic Energy Agency was notified, and a team was sent to recover the containers at the campsite, discovering that they were Soviet-era radiothermal penetrators containing 40,000 curies of strontium. The amount of radiation was said to be equivalent to that released in the immediate aftermath of the catastrophic nuclear accident at Chernobyl in Ukraine.

U.S. officials at the time thought the generators had been stolen by Chechen rebels who were then operating in Georgia’s Pankisi Gorge and transporting them to other rebel-occupied areas.

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