Witnesses have described scenes of pandemonium after a powerful blast tore through a packed stadium in Grozny.
The crowds of spectators fled in panic
The stadium's VIP section, where the device was planted, immediately collapsed, sending up plumes of smokes.
Terrified people screamed in panic, as security forces - also apparently seized by the chaos - fired shots in the air over the crowd, witnesses said.
Russia's NTV television showed one man running away from the blast with an unconscious and bleeding boy.
Another victim - an old man with blood pouring thorough a bandage on his head - was helped away to the stadium's exit.
Just moments after the blast, Moscow-backed Chechen President Akhmad Kadyrov - who was sitting in the top row of the VIP stand - was seen still apparently conscious, with blood pouring from his head.
Several vehicles with security officers raced to the stand to help the president to hospital, eyewitnesses said.
The pictures from Grozny sent shockwaves throughout Russia
Footage by NTV later showed men in uniform carrying a man resembling Mr Kadyrov away from the destroyed VIP stand. Mr Kadyrov later died of his wounds in hospital.
"During the explosion, Kadyrov was hit in the head, shoulders and legs," Chechen interior ministry spokesman Tauz Dzhabrailov, who was himself injured in the attack, later told the AFP news agency.
Eyewitnesses said the device went off during a concert to mark victory in World War II at about 1035 local time (0635GMT) - after the official speeches by Chechen top officials were over.
A popular local singer - who was performing on stage when the device went off - was also seriously injured.
Russian officials claimed the device was hidden inside a concrete block of the stadium.
They said it explained why it was not detected the previous night and also on Sunday morning when the Dynamo stadium was combed by security officials.