Moscow police went on alert Wednesday after a shock car bombing injured 29 people in Pyatigorsk, a southern city that acts as headquarters for the North Caucasus Federal District.
Police said they were closely monitoring railway and metro stations, airports and other public places, and searching buses arriving from the country's south.
A bomb scare prompted the evacuation of about 1,000 people from the World Trade Center Moscow and the adjacent Crowne Plaza Hotel on 12 Krasnopresnenskaya Naberezhnaya.
Bomb experts with sniffer dogs searched the center after an anonymous phone tip but found no explosives, RIA-Novosti reported.
The heightened alert in Moscow came after a Lada car loaded with explosives equivalent to 40 kilograms of TNT blew up on Tuesday near a cafe in downtown Pyatigorsk, a Stavropol region resort with a population of 208,000 that had not been touched by the violence raging in the surrounding North Caucasus in recent years.
The blast left a two-meter-wide hole in the ground. Photos from the site showed a scorched and twisted car frame and buildings with windows shattered by the blast's wave.
The 29 people injured in the attack were cafe customers and passers-by, officials said. Four people hospitalized with serious injuries were airlifted to Moscow hospitals.
The head of the Investigative Committee, Alexander Bastrykin, flew to Pyatigorsk on Wednesday to oversee the investigation after President Dmitry Medvedev ordered the Federal Security Service and the Prosecutor General's Office to identify and capture those responsible.
No one has claimed responsibility for the bombing, which the authorities have declared a terrorist attack.
Stavropol regional police have initiated a special operation to nab the attackers, RIA-Novosti reported Wednesday.
The owner of the car has been identified as Alexander Kim, 42, a Stavropol region resident, but he is not considered a suspect in the case, investigators said, adding that Kim's whereabouts could not be established Wednesday.
Anatoly Safonov, the Kremlin's anti-terrorism adviser, said Islamist militants affiliated with Chechen rebel leader Doku Umarov might have carried out the attack.
Umarov's rebels claimed responsibility for a small explosion near Gazprom's headquarters in southern Moscow last week, but only three days after the bomb detonated. No one was injured.
Umarov also claimed responsibility for the twin suicide bombings that killed 40 people in Moscow's metro in March. In June, the United States put him on the list of international terrorists.
Umarov said he was stepping down as the insurgents' leader in an online video on Aug. 2, but he later backtracked on the statement, saying he changed his mind "in connection with the situation shaping up in the Caucasus."
Analysts say his resignation attempt might reflect a split within the rebel community.
But Safonov said the Pyatigorsk bombing might have nothing to do with any power struggle.
"It's possible that the attack had been planned long before the split," he said, RIA-Novosti reported.
Meanwhile, Vladimir Zhirinovsky, leader of the Liberal Democratic Party, said the attackers might have received help from unspecified foreign powers. "The external enemy does not sleep," Zhirinovsky said, without elaborating.
He said in a statement that the attack was supposed to “scare” people and inflame tensions between ethnic Russians and people of other ethnicities, as well as inspire hatred against the authorities.