MOSCOW (AP) — Two suicide bombings in as many days have killed 31 people and raised concerns that Islamic militants have begun a terrorist campaign in Russia that could stretch into the Sochi Olympics in February. Russian and international Olympic officials insisted the site of the games, protected by layers of security, is completely safe.
The attacks in Volgograd, about 400 miles (650 kilometers) from Sochi, reflected the Kremlin's inability to uproot Islamist insurgents in the Caucasus who have vowed to derail the games, the pet project of President Vladimir Putin.
No one has claimed responsibility for Sunday's blast at the Volgograd railway station or Monday's bus explosion in the city, but they came only months after Chechen rebel leader Doku Umarov threatened new attacks on civilian targets in Russia, including the Olympics.
In addition to the dead, the bombings wounded 104 people, according to Russia's Health Ministry. As of late Monday, 58 remained hospitalized, many in grave condition.
Suicide bombings have rocked Russia for years, but the insurgents seeking to create an Islamic state have largely confined their attacks to the North Caucasus region in recent years. The blasts in Volgograd signaled that militants want to show their reach outside their native region.
Matthew Clements, an analyst at Jane's, said Caucasus militants could be targeting major transportation hubs like Volgograd to embarrass the Kremlin and discourage attendance at the Feb. 7-23 Olympics.
"The attack demonstrates the militants' capability to strike at soft targets such as transport infrastructure outside of their usual area of operations in the North Caucasus," he said in a note. "Although the very strict security measures which will be in place at the Sochi Games will make it difficult to undertake a successful attack against the main Olympic venues, public transport infrastructure in Sochi and the surrounding Krasnodar territory will face an elevated risk of attack."
Some experts say the perpetrators could also have been targeting Russia's pride by hitting the city formerly called Stalingrad, which is known for the historic battle that turned the tide against Nazi Germany.
"Volgograd, a symbol of Russia's suffering and victory in World War II, has been singled out by the terrorist leaders precisely because of its status in people's minds," Dmitry Trenin, the head of the Carnegie Endowment's Moscow office, said in a commentary on the organization's website.
A city of 1 million northeast of Sochi, Volgograd is a hub with railway lines running in five directions across the country and numerous bus routes connecting it to the volatile Caucasus provinces.
Security checks on buses have remained largely symbolic and easily avoidable, making them the transport of choice for terrorists in the region. And tighter railway security isn't always enough to prevent casualties. In Sunday's attack, a suicide bomber detonated an explosive in front of the train station's metal detectors, killing 17 people, including the attacker.
Security at Russia's railway stations and airports has been tightened after a male suicide bomber hit Moscow's Domodedovo Airport in January 2011, killing 37 people and injuring more than 180. Two bombings on the Moscow subway in March 2010 by female suicide bombers killed 40 people and wounded more than 120.
Umarov, who had claimed responsibility for the 2010 and 2011 bombings, ordered a halt to attacks on civilian targets during the mass demonstrations against Putin in the winter of 2011-12. He reversed that order in July, urging his men to "do their utmost to derail" the Sochi Olympics, which he described as "satanic dances on the bones of our ancestors."
Aware of the threat, the Sochi organizers have introduced some of the most extensive identity checks and sweeping security measures ever seen at an international sports event.
Anyone wanting to attend the games will have to buy a ticket online from the organizers and obtain a "spectator pass" for access. Doing so will require providing passport details that allow authorities to screen all visitors.
The security zone created around Sochi stretches approximately 100 kilometers (60 miles) along the Black Sea coast and up to 40 kilometers (25 miles) inland. Russian forces including special troops will patrol the forested mountains flanking the resort and use drones to keep a constant watch over Olympic facilities. Speedboats will patrol the coast and sophisticated sonar will be used to detect submarines.