A suicide attack on a trolleybus in the Russian city of Volgograd killed at least 14 and wounded at least 28 people on Monday, following a strike near the city's main train station that left 17 dead and more than 40 injured the day before. On Friday, three people were killed in the city of Pyatigorsk. Monday's bombing is the third to hit Volgograd in three months.

The strikes have left Volgograd residents shaken and authorities fearing a wave of attacks ahead of the Sochi Winter Olympic Games, set to begin on February 7. (Volgograd is just 600 miles from Sochi.) One woman near the blast commented to Reuters, ""For the second day, we are dying – it's a nightmare," adding that the focus on public transit is affecting daily routine, "What are we supposed to do – just walk now?" Reuters reports a grisly scene at the site of the attack:

Monday's blast was so powerful it blew out the third-story windows of a nearby apartment building, and witnesses said passengers were flung from the bus by the blast. "We ran outside. There was smoke and people were lying in the street. The driver was thrown far. She was alive and moaning ... Her hands and clothes were bloody," said Olga, a clerk in a shop near the scene of the blast.

Responsibility for either of the attacks has not yet been claimed, but a Chechen insurgent group hoping to build an Islamic state in the country's north Caucasus region vowed in July to disrupt the Olympics, and is suspected of orchestrating the strikes.

Volgograd, formerly Stalingrad, was the site of the Battle of Stalingrad during World War Two, a strategic battle that marked the beginning of the end for Nazi forces. The Associated Press notes that the Carnegie Endowment's Moscow head, Dmitri Trenin, wrote on the organization's website that the city has been targeted for its historic significance: "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." The city is also a central transportation point, according to the AP

Volgograd, located about 650 kilometers (400 miles) northeast of Sochi, serves as a key transport hub for southern Russia, with numerous bus routes linking it to volatile provinces in Russia's North Caucasus, where insurgents have been seeking an Islamic state.

Anti-terrorism expert Alexei Filatov told Reuters that cities like Volgograd – which lost police officers to Sochi, where Russian President Vladimir Putin is increasing security ahead of the Games – are especially vulnerable to terrorist strikes and can expect more in the coming weeks. "The threat is greatest now because it is when terrorists can make the biggest impression," he said.