Appearing on Russian state television, the unidentified man said the attack was ordered by Chechen rebel leader Aslan Maskhadov and Chechen warlord Shamil Basayev.
"They gathered us in the woods and 'The Colonel' said that we should take over a school in Beslan. That was our order," he said.
At least 338 hostages, including 156 children, were killed after terrorists seized the school building and held more than 1,000 students and adults hostage.
Along with them, 26 hostage-takers and 10 Russian special forces died.
Ten of the slain hostage-takers were from Arab countries, authorities have said.
"When we asked why we were doing this, what our goal was, 'The Colonel' answered us, 'Because we need to start a war across the Caucasus."
He said the hostage-takers included Uzbeks, Arabs and Chechens.
