Two deadly car bomb explosions have hit Makhachkala, the capital of Russia's North Caucasus republic of Daghestan.
The explosions occurred on May 20 outside a court building in the city.
A spokesman for Daghestan's Interior Ministry, Vyacheslav Gasanov, says nobody was hurt when the first car exploded outside the headquarters of the court's bailiffs' directorate.
A second blast then went off after police officers arrived at the scene, killing at least four people.
More than 40 people were injured. Some 20 vehicles were damaged by the blast.
Police estimated that the second bomb comprised between 40 and 50 kilograms of TNT.
The local Interior Ministry said there was also one child among those injured. At least 11 of the injured were reported to be in a serious condition in hospital.
Investigators said it appeared that both explosions were set off by remote control.
No one has claimed responsibility for the attacks.
Vladimir Markin, the spokesman for Russia's Investigative Committee, described the blasts as a "terrorist act."
Two separatist wars in neighboring Chechnya have killed tens of thousands of people and spawned an Islamic insurgency that has engulfed the entire North Caucasus region in Russia's south.
The region sees almost daily attacks on police and federal officials claimed by or blamed on Islamist insurgents.
Daghestan, an ethnically mixed, predominantly Muslim region between Chechnya and the Caspian Sea, has become the most violent province in the North Caucasus.
Insurgents say they are fighting to carve an Islamic state out of southern Russia.
The rebels have often sought to increase casualties by setting off an initial blast to attract law enforcement officers and then detonating a second bomb.
With reporting by AP, Reuters, RIA-Novosti, Interfax, and ITAR-TASS