President Dmitry Medvedev promised on Thursday to "destroy" those responsible for this week's bombing outside a cafe in the southern city of Pyatigorsk that injured 30 people.
"All those involved must be found. … If they put up resistance, they must be destroyed," Medvedev said during a visit to Pyatigorsk, Interfax reported.
No one has claimed responsibility for Tuesday's bombing.
Investigators said Thursday that the owner of the car used in the attack remains missing and was probably killed by Islamist militants. The owner, taxi driver Alexander Kim, has no known links to militants and is wanted as a witness, not a suspect, they said.
Unidentified Stavropol region police officials told Kommersant that the attackers probably hired Kim as a driver and killed him for his car.
Medvedev on Thursday also visited a Pyatigorsk hospital where 15 people injured in the explosion are being treated. He ordered state-of-the-art medical equipment to be supplied to the hospital.
Victims will receive compensation of 200,000 to 400,000 rubles each ($6,500 to $13,100), depending on the severity of their injuries, local officials said Thursday, RIA-Novosti reported.