A suicide bomber has blown herself up beside a police car in Grozny, the capital of Russia's southern region of Chechnya, wounding six people.
Russian news agencies carried conflicting reports on the number of people who suffered in the blast, but local officials said there were no fatalities.
Speaking at the scene of the blast, Ruslan Alkhanov, the Chechen interior minister, said: "I officially declare there were no victims in the explosion.
"Two Chechen policemen and four civilians were wounded."
A mangled, burnt-out carcass was all that remained of the police car at an intersection in Grozny's usually bustling centre, a reporter from the Reuters news agency said.
A passenger minibus with shattered windows was seen nearby.
A series of attacks by Islamist fighters on security forces and local leaders over recent months has shattered several years of relative calm and raised questions about the Moscow's control of the north Caucasus region.
Leaders from across the area warned Dmitry Medvedev, the Russian president, last month that they were struggling to contain the violence which they said had permeated all spheres of society.
Russia has fought two wars against Chechen separatists since the early 1990s.