At least 10 people were killed in a terrorist attack on a trolleybus on Monday in the Russian city of Volgograd, a day after a suicide bomber claimed 17 lives in the main railway station of the southern city.
The successive blasts, just 40 days before Russia is to hold the Winter Olympics in the Black Sea resort of Sochi, will raise fears of further terror attacks. Sochi is about 430 miles (690 km) southwest of Volgograd.
The following GIF supposedly shows the moment the blast on Sunday:
Though it was initially reported that the station attack was carried out by a female bomber, later evidence suggested that both a woman and a man were involved. Around 37 people were hospitalized after Sunday's attack and 23 were reported wounded on Monday.
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Though no one has claimed responsibility for either of the attacks which left dozens wounded in addition to the deaths, it is being widely speculated that these are attempts by Chechen Islamist separatist groups to halt the Sochi Games.
The Russian Federation forces attacked North Caucasus republics of Chechnya, Dagestan, andIngushetia in August 1999, an event known as the Second Chechen War, to wipe out Islamists attempting to form a separate Muslim state or emirate.
Although Russia ended its decade-long "counter-terrorism operation" against separatist rebels in 2009, insurgency is still entrenched in the Muslim-dominated region of North Caucasus. Militants seek to destabilize the government responsible for attacking Chechnya.
In a Web-posted video released in July, insurgents threatened to use "maximum force" to prevent them from being held. There are reports of both Chechen men and women who will attempt to create disruption in Russia through use of violence.
"We can expect more such attacks. The threat is greatest now because it is when terrorists can make the biggest impression. The security measures were beefed up long ago around Sochi, so terrorists will strike instead in these nearby cities like Volgograd,"Alexei Filatov, deputy head of the veterans' association of the elite Alfa anti-terrorism unit, told Reuters
The Sochi Olympics have been regarded as a major prestige project for President Vladimir Putin who agreed to allow gay athletes in the country for the event despite the fact that Russia recently passed a law banning homosexuality and their proponents.
In addition, Volgograd, the city that underwent two explosions in two days, is one of the venues for another high-profile sports event; the soccer World Cup due to be held in 2018.