Chechen President Akhmad Kadyrov was among 14 people killed and 38 injured in a landmine explosion in the Dynamo Stadium in the Chechen capital, Grozny, the emergency ministry said on Sunday.
A ceremony marking victory in World War II was being held at the stadium.
Top Russian regional commander Valery Baranov was seriously injured and is undergoing an operation, Radio Mayak quoted the ministry spokesperson as saying.
The explosion, which was triggered under a VIP seat, critically injured Kadyrov, who died 30 minutes later.
A Reuters photojournalist also reportedly died in the attack.
Russian President Vladimir Putin vowed retaliation. "There can be no doubt that payback is inevitable against those whom we are fighting today. It will be inevitable for the terrorists," RIA Novosti news agency quoted him as saying.
The attack appeared to be triggered by Chechen separatists. It is an apparent sign to show that the Chechen resistance against Russian rule is still active.