Russian forces say Chechen rebel leader Aslan Maskhadov has been killed.
Russia blamed Maskhadov for a series of attacks
Russian television showed pictures of a body resembling that of Mr Maskhadov, 53, in a pool of blood in Chechnya.
President Vladimir Putin has asked for further identification. However, Mr Maskhadov's envoy in London, Akhmed Zakayev, later confirmed the death.
Mr Zakayev said resistance in Chechnya would continue despite the death of Mr Maskhadov, seen as the most moderate of Chechnya's rebel commanders.
Mr Maskhadov was elected Chechen president in January 1997 but was ousted two years later.
Thousands of people - many of them civilians - have been killed in the 10-year war between Russian forces and Chechen separatists.
Few details have been released of the Russian operation at the settlement of Tolstoy-Yurt, near the Chechen capital, Grozny.
Gen Ilya Shabalkin, a spokesman for Russian forces in the Caucasus region, earlier told news agencies that Mr Maskhadov's body had been found in a bunker.
But it was not clear whether he had been killed by Russian forces.
Chechnya's Moscow-appointed Deputy Prime Minister Ramzan Kadyrov told Interfax news agency the intention had been to take Mr Maskhadov alive, but he had been killed as a result of his bodyguards' carelessness in handling their weapons.
Russia's FSB security chief briefed President Putin on the troops' operation in a Chechen village, but did not say how Mr Maskhadov was killed.
He told the president the FSB security services "today carried out an operation in the settlement of Tolstoy-Yurt, as a result of which the international terrorist and leader of armed groups Maskhadov was killed, and his closest comrades-in-arms detained".
"Carry out additional identification tests, report back," Mr Putin ordered.
"If this information is confirmed, grant state awards to all those involved in the operation," the Russian leader said.
"We have to gather our forces to protect the people of the republic and citizens of all Russia from the bandits," Mr Putin said.
Russian also television showed pictures of a grey-bearded and shirtless corpse in a pool of blood.
If the death is confirmed, this will be a major coup for Moscow, the BBC's Sarah Rainsford in Moscow says.
Moscow has blamed Mr Maskhadov for a string of deadly attacks in Russia, including a rebel attack on a school in the south Russian town of Beslan last September in which more than 330 hostages - half of them children - died.
He led the Chechen separatists who defeated Russian forces in a 1994-1996 war.
Mr Putin sent Russian troops back into Chechnya in October 1999.