Russian President Vladimir Putin has vowed to fight “terrorists until their complete annihilation”, in his first comment on two suicide attacks in the southern city of Volgograd.
The attacks, on Sunday and Monday, claimed a total of 34 lives.
Thousands of police are patrolling public transport and checking traffic in the city following the attacks, which injured some 60 people.
The first victim has been buried – a policeman killed at the train station.
No group has said it carried out the attacks, which Russian investigators believe are connected. They are similar to previous indiscriminate attacks by Islamist militants operating from the North Caucasus.
AnalysisOleg BoldyrevBBC Russian, Volgograd
Volgograd’s streets are buzzing with special buses that carry police and military patrols. Soldiers are in full battle gear with helmets and bulletproof vests.
At the entrance to a large shopping mall police asked everyone to open their bags and unbutton coats. Everyone was treated with respect and people, mostly sales assistants queuing to get inside, were very patient.
However, one could immediately see many issues here. How long will the queue be when the shopping mall opens to the public? Is not such a gathering of people in a single place a security problem?
Some residents say new security measures, however chaotic, bring some relief. Others are quite sceptical. They doubt that policemen and soldiers will be able to find a bomber in the crowd. But almost everyone I spoke to said they wished these measures had been introduced in October, after the first bomb attack on a bus.
Volgograd, a city of one million known as Stalingrad during World War II, commemorated the 70th anniversary of the battle of the same name this year, in an outpouring of Russian patriotic fervour.