Renamo, Mozambique's main opposition movement, has rejected provisional results showing the ruling Frelimo party won Wednesday's presidential and parliamentary elections, saying they were flawed by fraud and demanding a fresh vote.
Results released on Thursday night showed that Defence Minister Felipe Nyusi, Frelimo's presidential presidential candidate, had 63 percent of the vote after counts at almost a quarter of 17,000 polling stations.
Renamo candidate Afonso Dhlakama was second with nearly 30 percent of the vote.
"We don't accept the results," Renamo spokesman Antonio Muchanga told the Reuters news agency on Friday. "The results should be annulled and new elections held."
Muchanga spoke shortly after African election monitors endorsed the vote as largely peaceful and free.
Daviz Simango, leader of a newer party called the Mozambique Democratic Movement, was placed third on 7.5 percent.
Renamo has lost all elections since the end of the country's 16-year civil war in 1992.
Its supporters have clashed with security forces in recent years, but violence ended after Renamo signed a peace deal in September.
The country's discovery of large gas and coal reserves has attracted international investment, giving hope to the country's infrastructure.
"Investors are watching Mozambique closely and want stability and predictability," said Chatham House researcher Alex Vines, describing the election as the "most important" since the first post-war vote in 1994.