At least 13 supporters of Nigeria Premier League club, Ocean Boys, are believed to have been killed while several others were injured in a clash between rival cult factions in the country's oil-rich Bayelsa state.

Club officials refused to comment on the incident.

"The media officer of Ocean Boys could not confirm or deny the incident," disclosed an official of the Nigeria Premier League, Tunji Babalola.

However, according to local media reports Sunday, clashes between the rival cult gangs - Icelanders and Greenlanders - began on Friday, when a member of the supporters club of Ocean Boys, who belongs to one of the gangs, was shot dead in the Bayelsa State capital, Yenagoa.

Later that night, a reprisal attack at a popular night club in the city left a member of another gang dead and several cars riddled with bullets.

However, as the team and their supporters headed for a league game in Ughelli in nearby Delta State, gunmen, riding in a black sports utility vehicle, reportedly opened fire on the bus, killing seven persons instantly. Three others died later.

Survivors said the same vehicle was spotted at the scene of the reprisal attack at the night club on Friday.

On Saturday, Ocean Boys defeated league leaders Bayelsa United 1-0.