More than 30 people have been killed in two successive bomb blasts in the Russian city of Volgograd over the last two days, including 14 in a suicide bombing on a bus during rush hour Monday morning.
The attacks come roughly a month before Russia hosts the 2014 Winter Olympics in Sochi, where security forces remain on high alert. Russians throughout the country remain fearful of further attacks, including the roughly 1 million in Volgograd, 400 miles northeast of Sochi.
No group has yet claimed credit for the attacks, reports The Associated Press. Russian authorities believe a male suicide bomber carried out Monday's attack and that it was linked to a similar strike on a Volgograd railway station on Sunday.
"Now we can say that the bomb was detonated by a suicide bomber, a man. Fragments of his body had been recovered and sent to genetic examination to establish his identity," said Vladimir Markin, a spokesman for the investigative committee, according to Russian-based Pravda News.
Chechen rebel leader Doku Umarov has threatened in recent months to conduct attacks on new targets in Russia, including in Sochi, ahead of the planned winter Olympic.
The "strike elements" packed into both bombs are identical, he said.
"It confirms the version of our investigation saying that the two attacks were related to each other," Markin said. "Perhaps they could be prepared in one place."
Official state news service RIA Novosti reports the electric trolleybus was packed with commuters when the bomb detonated at roughly 8:10 a.m. local time. Debris was strewn across the street around the blackened frame of the bus. Its roof and windows were blown out.
The blast also blew out windows of nearby homes.
Fear has spread throughout the country. Red Square was evacuated for a short time after a woman dropped a bag and ran away, according to RIA Novosti. Russian President Vladimir Putin has ordered a heightened security stance, and has sent federal law enforcement officers to help with the aftermath of the Volgograd attacks.
The Russian Emergency Situations Ministry plans to pay roughly 1 million rubles, more than $300,000, to each of the families of the people killed in the attack. Families of those who were injured will each receive between 200,000 and 400,000 rubles, or $6,000 to $12,000.
The U.S. condemned the attack in "the strongest possible terms."
"We send our sincere condolences to the families of the victims," wrote State Department spokeswoman Jen Psaki in a statement Monday, "and stand in solidarity with the Russian people against terrorism of any kind."
U.N. Secretary General Ban Ki-moon also condemned the attacks and called on the perpetrators to be brought to justice.
"He stands in solidarity with the Russian Federation in the face of terrorism," his spokesman said.
The 15 members of the U.N. Security Council, of which Russia is a permanent member, issued a joint statement, decrying the attacks as heinous and expressing their sympathy to the victims:
"The members of the Security Council reaffirmed that terrorism in all its forms and manifestations constitutes one of the most serious threats to international peace and security, and that any acts of terrorism are criminal and unjustifiable, regardless of their motivation, wherever, whenever and by whomsoever committed."