Russian Deputy Emergency Minister Vladimir Stepanov said officials are on high alert and prepared for another attack, given the Russian New Year is only a few days away and the 2014 Winter Olympics in Sochi kick off Feb. 7, Euronews.com reported.
"A state of emergency was introduced in Volgograd yesterday [Sunday], so all the organizations and services are working on this," Stepanov said. "But, as I have already said, to ensure security during the holiday period, the entire emergencies ministry has been put on high alert."
At least 14 people were killed in the trolleybus bomb blast Monday. The day before, 17 people were killed in another bomb explosion at a railway station. Russian investigation officials said suicide bombers likely were behind the two incidents and were testing the DNA from the suspected bombers' remains collected at both scenes.
Terrorist incidents have been persistent in southern Russia despite efforts to step up security ahead of the Olympic Games in Sochi, about 430 miles from Volgograd, RIA Novosti said.
International Olympic Committee President Thomas Bach issued a statement "utterly condemning" the "despicable attack on innocent people."
"Sadly, terrorism is a global disease but it must never be allowed to triumph," he said.
"The Olympic Games are about bringing people from all backgrounds and beliefs together to overcome our differences in a peaceful way. The many declarations of support and solidarity from the international community make me confident that this message of tolerance will also be delivered by the Olympic Winter Games in Sochi."
In Washington, a statement issued by National Security Council representative Caitlin Hayden condemned the attacks and offered security assistance for the Winter Games.
"The United States stands in solidarity with the Russian people against terrorism," the statement said. "The U.S. government has offered our full support to the Russian government in security preparations for the Sochi Olympic Games, and we would welcome the opportunity for closer cooperation for the safety of the athletes, spectators, and other participants."
The U.N. Security Council expressed outraged over the trolleybus and railway station attacks.
"These abhorrent and abominable attacks deliberately targeted places of mass gathering, in particular public transportation," the Security Council said in a statement, noting the need to bring those responsible for Monday's "reprehensible act of terrorism to justice."
A blanket protected an 8-month-old baby from life-threatening burns in the trolleybus explosion even though the attack killed the child's mother and grandmother, RT reported. The infant, in a coma, was listed in critical condition at a nearby hospital.
Students from Volgograd's universities volunteered to assist those injured in the trolleybus blast, helping nurses and medics at the hospital, RT reported. Also, several businesses in the city once known as Stalingrad provided commuters with transportation to work.
Meanwhile, a charity campaign has been started by the Volgograd Charity Foundation has started a charity campaign and the Spiritual Administration of Muslims in Moscow launched a fundraising effort for the families of the bombing victims, RT reported.
Russian authorities said 1 million rubles (about $30,400) will be given to the families of those who were killed in the trolleybus explosion. Relatives of those injured will receive between 200,000 and 400,000 rubles ($6,000-$12,000), depending on the injuries.
Russian President Vladimir Putin ordered security tightened in Volgograd, Moscow and elsewhere, and met with leaders of the Federal Security Service and Interior Ministry Monday.
RIA Novosti said video footage broadcast by TV station Rossiya-24 showed the blackened shell of the vehicle with its roof blown outward by the explosion and debris scattered across the street.
Russia's National Anti-Terrorism Committee said it appeared the explosive device was placed in the vehicle's passenger cabin.
In October, six people were killed and 37 injured in a terrorist attack in Volgograd when a bomb carried by a woman from Dagestan exploded as she traveled on a commuter bus.