Authorities in Thailand have arrested two men following a bomb blast at a festival near the border with Myanmar that killed three people and wounded dozens, police said on Saturday.

An improvised explosive device went off on a dance floor at a festival in Umphang district in Thailand’s northern Tak province on Friday night, according to local police.

Two people were killed instantly and another died later in hospital, police said.

The explosion also injured 48 people among approximately 8,000-9,000 attending the event.

Thai police said they had arrested a Thai youth and a man they said was a member of the Karen National Union (KNU), an ethnic minority rebel group that has fought the Myanmar military for decades for autonomy in neighbouring Myanmar’s Karen state.

Tak police chief Major-General Samrit Ekamol said the Myanmar suspect had thrown the bomb after encountering a “rival gangster” he had previously fought with.

A senior KNU official contacted by AFP, who declined to be named as he was not authorised to speak to the media, denied any involvement and said the group did not have any members in the area.

The KNU can call on more than 5,000 fighters, maintains close links with Thai police and military, and has extensive business interests on both sides of the border, according to analysts.

Thai Prime Minister Paetongtarn Shinawatra expressed her condolences to the victims and their families, and urged security agencies to carry out an investigation.