Former Chechen President Zelimkhan
Yanderbiyev has been killed in an explosion in Qatar.
Yanderbiyev had just returned to his car after attending Friday prayers
The satellite TV station al-Jazeera said Mr Yanderbiyev's car was hit by a blast in the capital, Doha.
Two of his bodyguards were reportedly killed and his teenage son, Daud, is said to have been seriously injured in the blast.
Yanderbiyev was mentioned on a UN list of groups and people with suspected links to the al-Qaeda organisation.
A hospital spokesman said Mr Yanderbiyev was leaving a mosque after Friday prayers in Doha's northern Dasma district when the blast occurred.
A spokesman for the Chechen rebels, Movladi Udugov, has accused the Russian special services of involvement in the blast.
But Russia's Foreign Intelligence Service (SVR) has denied any involvement.
The service "has not taken part in such actions since 1959," when a Soviet KGB agent in Munich assassinated Stepan Bandera, a Ukrainian nationalist, a spokesman for the service, Boris Labusov, was quoted as saying.
Mr Yanderbiyev was acting Chechen president in 1996.
He headed the rebel delegation which held talks with Russian President Boris Yeltsin and Prime Minister Viktor Chernomyrdin in the same year.
He has been included on the Interpol wanted list since 2001.
The leader of Chechnya's pro-Moscow administration President Akhmad Kadyrov told Russia's Interfax news agency: "Yanderbiyev was the chief ideologue of the separatists and later of their terrorist organisations.
"You will find no one in Chechnya who will regret what happened to Yanderbiyev."
The former Chechen leader had been living in Qatar for three years and Moscow repeatedly sought his extradition.
He was viewed as a key figure behind the 1999 Chechen incursion into Dagestan.
He was also suspected of links to the siege of a Moscow theatre in October 2002 that left 130 hostages dead.
Mr Yanderbiyev was considered a key link in the Chechen rebels' fundraising network from abroad.