BANGKOK - Four people were killed and scores injured on Monday in a hand grenade explosion at a concert in northeastern Thailand, police said.

The incident occurred early Monday in Maha Sarakham province's Nadoon district where a famous local band was performing in celebration of a religious festival, according to Kritchai Saruamsri, superintendent of Nadoon police station.

He said a man carrying a suspicious object run from the crowd of audience and as the police approached him, they found that he was holding an M67 grenade with its safety pin already removed.

The man, who was later identified as 31-year-old Winai Jed-ngam, dropped the grenade, it bounced off the floor and exploded.

Four men, including two police officers and two civilians, were killed in the blast and about 50 others injured, including the attacker. One member of the band was also reportedly wounded.

Police were investigating the motive for the attack, saying it might be related to the ongoing dispute between local rival gangs.