A suspected suicide bomber has blown up a truck outside security offices near rebel Chechnya, killing at least three people in a fresh setback for Moscow's peace plan for the region.
The truck packed with explosives detonated at the headquarters of Russia's FSB security service in Magas, capital of Ingushetia - a tiny Russian province adjoining Chechnya.
"It was clearly an act of terror," Deputy Prosecutor General Sergei Fridinsky told Itar-Tass news agency.
"According to our preliminary theory, it was a truck driven by a suicide bomber that exploded near the building."
The blast occurred in the middle of campaigning for an October 5 election for Chechen president - centre-piece of President Vladimir Putin's plan to bring peace to the region. Moscow refuses to talk to separatists, excluded from the poll.
Russian television showed virtually all windows shattered and the roof badly damaged in the three-storey building. Commentators said casualties would have been far greater had the walls not withstood the blast. The lavish headquarters of the Ingush president across the street was also damaged.
An Ingush Interior Ministry spokeswoman told journalists two people died in the noon explosion, while another died on the way to hospital and 24 were being treated for their injuries.
It was not immediately clear whether the truck driver was among the dead. No one claimed responsibility for the attack.
Extremists among separatists have resorted increasingly to suicide attacks, killing 150 people since April.
About 50 people died last month when a truck bomb exploded outside a hospital northwest of Chechnya treating soldiers near Russia's biggest base in the southern Caucasus region.
The recurring attacks make a mockery of Kremlin claims to control Chechnya four years after its troops returned to the region. That operation, a key factor in securing Putin's 2000 election victory, ended three years of de facto independence.
Tens of thousands of Russian servicemen stationed in Chechnya remain subject to daily attacks, with many districts outside the capital no-go areas, particularly at night.
Commentators linked the latest blast to the local election.
"Hardline rebels who are ignoring the elections want to demonstrate that they are prepared to fight for their country," Konstantin Zatulin, director of Russia's Institute of CIS states, told Ekho Moskvy radio.
The election became what amounted to a one-horse race last week with the pullout of two rivals of Akhmad Kadyrov - head of the local administration and the Kremlin's preferred candidate.