West African nations on Thursday recognized Umaro Sissoco Embalo as president of Guinea-Bissau, after four months of dispute over whether his election was fraudulent.
Embalo won a run-off presidential vote in the chronically unstable country in December, according to the country's electoral authority.
But losing candidate Domingos Simoes Pereira, from the long-ruling PAIGC party, called the election fraudulent and took the case to the Supreme Court, which has not yet ruled.
Embalo, a former prime minister, declared himself president in February without waiting for the court, creating a political impasse.
The heads of state of Economic Community of West African States (ECOWAS) said in a statement that they recognized Embalo as president but also called for constitutional reform to be put to a referendum within six months.
Experts have argued that the country's semi-presidential system contributes to its instability, with frequent clashes between the president and the prime minister.
Guinea-Bissau has known little but coups and instability since its independence from Portugal in 1974.
The country has also long struggled with poverty and corruption and it has also become a transit route for South American cocaine heading to Europe.