The fearsome rebel leader has been wanted by Russian authorities for years in connection with various attacks in Russia.

Basayev led the first Chechen mass hostage-taking inside Russia

Shamil Basayev, 39, has long threatened a series of "kamikaze" attacks inside Russia, arguing that Russian civilians were legitimate targets.

North Ossetian interior ministry spokesman Ismel Chaov has said: "You can assume it was Basayev, because Basayev is behind most of the terrorist acts."

He led the first Chechen mass hostage-taking in the southern Russian town of Budyonnovsk in 1995 and he claimed to have organised the seizing of a Moscow theatre in 2002, during which 129 people died.

He is believed to have been behind a stadium bomb attack in Chechnya's capital, Grozny, on 9 May that killed Moscow-backed President Kadyrov.

Most recently, Mr Basayev is said to have organised a series of attacks on government buildings and police stations in neighbouring Ingushetia in June, which left almost 100 people dead.

He has also boasted to have trained Chechen female suicide bombers - the infamous "Black Widows" brigade.

He is also suspected of having links with al-Qaeda operatives.

Moscow-educated Mr Basayev first rose to prominence shortly after Russian forces invaded Chechnya in 1994, when he became one of the leading commanders of the Chechen guerrillas.

"Russia is the last empire: it is built on blood," he said during a BBC interview several years ago.

When Russia was forced to withdraw its forces after the first Chechen war ended in 1996, Mr Basayev stood for president, but came second to Mr Maskhadov.

Mr Basayev also served briefly as prime minister in the self-proclaimed independent Chechen republic of Ichkeria in 1997.

Aslan Maskhadov, 52, has condemned the seizure of the school.

But he implicitly acknowledged Chechen involvement - by saying that acts of terror were carried out by people whose desire for revenge against acts of brutality by Russian troops had driven them out of their senses.

Maskhadov has condemed the school siege

Mr Maskhadov was born in exile in Kazakhstan and began his career as an officer in the Soviet army. After the collapse of the Soviet Union, he became breakaway Chechnya's chief of staff in 1992.

Mr Maskhadov led the Chechen forces which pushed the Russian army to retreat from Grozny in 1995.

At the same time, he was at the forefront of peace negotiations in 1995 and 1996, under which Moscow undertook to withdraw its forces from the republic.

Chechens elected him president in January 1997 because of his war record, and because he promised a more peaceful future than younger and more radical rival candidates, including Shamil Basayev.

On one point he was always firm, however: Chechnya must be independent.

He proved unable to control warlords, there were splits with rival rebel leaders and the republic descended further into crime and chaos.

When Chechen rebel forces crossed into Dagestan in 1999 and Moscow held Chechens responsible for a wave of bomb attacks across Russia, Russia accused him of having lost control and sent troops back into the republic.

When the Chechen president urged resistance, Moscow branded him a terrorist and withdrew its recognition of his presidency.

Mr Maskhadov was barred from standing in the elections of 2003 and 2004. Following the assassination of President Akhmad Kadyrov, he promised that the latter's successor could expect to meet the same fate soon after election.

Russia has also named several people it suspects of direct involvement in the siege.