The United States and its European allies could also be targets of suicide bombings like the back-to-back attacks in Russia that left at least 31 people dead and have Russian authorities reeling just weeks out from the 2014 Winter Olympics in Sochi, U.S. counterterrorism and defense experts said.
Jihadists in Syria revealed their plans to attack the Winter Olympics in a video released July 30, 2013. At least 31 people were killed and dozens injured in back-to-back attacks in Volgograd, Russia, Sunday and Monday. (Image via MEMRI)
There is also heightened concern that U.S. Olympians and spectators traveling to the region could be targets of Islamic radical groups looking for a Western target.
The two suicide bombings in the southern city of Volgograd, which also injured dozens, are still under investigation, but the terror threats were known for months by Russian authorities and counterterrorism officials. They came in the form of video from foreign jihadists fighting in Syria who pleaded with fighters to attack Russia and the Olympic games.
There has been no claim of responsibility for Sunday's explosion at a Volgograd railway station or for Monday's bus bombing near a busy market.
Russian President Vladamir Putin increased security in lieu of the games in Sochi, Russia but transit points leading into the city and other surrounding areas were not covered by the same security measures. Security challenges are heightened by the proximity of the games to Russia's North Caucasus, an area of known Islamic militant activity. There is also ongoing unrest in Chechnya -- also located near Sochi -- that threatens security for those attending the games.
A U.S. official with knowledge of the ongoing issues concerning the Olympics said there are "clearly sensitivities in our relationship with Moscow, but enhancing Olympic security and counterterrorism efforts more broadly are areas of clear mutual interest."
"The Volgograd bombings underscore the threat and the need to work hand-in-hand with Russia in order to ensure the protection of U.S. citizens participating in and attending the games in Sochi,” said the official, who spoke on condition of anonymity due to the sensitive nature of their work.
Steven Bucci, former assistant secretary of defense under Donald Rumsfeld and a senior defense analyst at the conservative Heritage Foundation said the terror bombings in Russia are a reminder that areas "outside of security perimeters are an enormously vulnerable target, and we have those in every airport on America. That worries me, that bad guys can go to school on these incidents and see the weaknesses in our system."
Russian law enforcement believe the attacks are the work of a Muslim radical group known as the Caucasus Emirate, whose leadership has already stated it will used "maximum force" to disrupt the games, news reports state.
In a July video, militants clad in black ski masks and brandishing automatic weapons vowed to make the Olympics a target of their retribution. TheBlaze recently published a video issued by leaders of one of Pakistan's most deadly terrorist networks threatening to send suicide fighters to New York City and Washington, D.C.
"If you cannot wage jihad in the mountains, wage it in the plains, but if, for some reason, you cannot do that either, then go to Moscow, to that hornet's nest of heresy, and wage jihad there," said Emir Saladin, a jihadist who joined other terror fighters in Syria. The video and translation were provided to TheBlaze by the Middle East Media Research Institute, a nonprofit organization that provides translation of media and reports out of the Middle East.
The terror leader warned Russian leaders that "you can choose any city in Russia you see fit, not only Moscow. Ultimately, you should prepare for the [Winter] Olympics in Sochi. There are concrete instructions from our Emir Dokka Abu Uthman to do so."
Jim Phillips, a terrorism expert with the Heritage Foundation, told TheBlaze that recent terror threats to the U.S. and its NATO allies need to be taken seriously, just as recent threats made by terror organizations to attack Russian interests during the Winter Olympics came to fruition this week. He added that targeting Olympic athletes or visitors would increase the terrorist organization's visibility but Russian security in Sochi will make it more likely that other cities will be targeted.
"I think especially after the Boston Marathon bombings, the U.S. can not afford to be complacent about the threat coming out of the Caucuses," said Phillips, referring to the Tsarnaev brothers suspected of setting off pressure cooker bombs at the marathon in April. "I think Americans may have become too complacent in recent years hopefully the Boston marathon bombings were a wake up call. We ignore this wake-up call at our own peril."
Tamarlen and Dzhorkar Tsarnaev were from Russia's Caucasus but were long-term U.S. residents. Older brother Tamerlen was killed during the police pursuit in Boston after the bombings, but evidence revealed that he visited his homeland of Dagestan -- an area believed to be the hub of Russia's radicalized Muslims -- in 2012, staying for six months.
Warnings from Russian intelligence suggesting he had been radicalized were not taken seriously by U.S. law enforcement.
Bucci warned that the Russian bombings are "worrisome on a couple of levels."
He said the Russians are pulling out all the security stops for Sochi, which "means they may be a little vulnerable elsewhere. I think our folks will be as secure as they can be. That said, they will make a hugely lucrative set of targets for the bad guys. What a win that would be for them, kill American infidels, embarrass Putin and the Russians, all around huge. It will be a tough target, and the Russians will [literally] kill to stop it from happening."
The Caucasus Emirate is a foreign terrorist group and the U.S. State Department has authorized a reward of up to $5 million for information leading to the location of its leader, Doku Umarov. According to the State Department, Umarov organized a suicide bombing outside the Chechen Interior Ministry in May 2009 and his group claimed responsibility for the 2011 bombing of Domodedovo Airport in Moscow, which killed 36 people.
The group was involved in the 2010 Moscow subway bombings that killed 40 people, and the 2009 bombing of the high-speed Nevsky Express train in which 28 people died.
In October, a female suicide bomber blew up a passenger bus in Volgograd, killing six people and wounding dozens more. News reports in the region claimed that the bomber was from Dagestan, where most of the militants are believed to be from, according to RIA Novosti on Monday.