The former governor of the Papua New Guinea province of Bougainville, John Momis, says he is seeking legal advice to challenge the results in a court of disputed returns.
He says he plans to sue the Provincial Election Manager, Mathias Pihei, for allegedly mismanaging the elections.
Mr Momis says there was massive foul play in the elections, especially in the Central and South Bougainville regions
The Bougainville People's Congress Party leader, Joseph Kabui, has been declared the winner at the weekend of the election for the first president of the Bougainville Autonomous Government.
Mr Kabui beat his nearest rival, John Momis, by about 14,000 votes
Mr Momis resigned from his post of governor to contest the elections.
A jubilant Mr Kabui said that 15 members of his party also won seats in the 39-seat assembly.
He named Joseph Watawi as his deputy and Magdalene Toroansi as the women's deputy in the caretaker cabinet.
Mr Kabui said he would announce the full cabinet in Arawa on Friday.
Mr Kabui said the successful elections and the declaration were the making of history for Bougainville and Papua New Guinea.