The military announced on Wednesday it had taken over the West African nation. Later, the opposition leader accused the incumbent president of staging the coup d’état to try to retain power.

Gunfire rang out near the presidential palace and national electoral commission headquarters on Wednesday afternoon, prompting confusion across Bissau, the capital.

Then, in a scene that has become familiar during the spate of coup d’états across West Africa in recent years, a military spokesman went on state television surrounded by heavily armed, uniformed men. He announced that they had deposed President Umaro Sissoco Embaló, closed the country’s borders and airspace and suspended the electoral process. He also announced a curfew and declared a state of emergency.

The statement from Mr. N’Tchama came shortly after the opposition candidate, Fernando Dias, made an impassioned speech claiming to have won Sunday’s election, and saying that he was only waiting for the final announcement of the national electoral commission on Thursday.

“We will go out into the streets to say thank you to all the people of Guinea-Bissau for all that they have done,” he told a crowd of supporters.

Mr. Dias is supported by an opposition coalition that includes the country’s largest party, the African Party for the Independence of Guinea and Cape Verde. That party and its leader, Domingos Simões Pereira, a former prime minister, were barred from running in last week’s election.

After the military takeover on Wednesday, Mr. Pereira’s nephew, Edson Pereira, said that his uncle had been arrested and was being held in a prison in Bissau.

After armed clashes broke out in December 2023 between military forces and the national guard, Mr. Embaló, who was out of the country at the time, declared a coup had been attempted against his presidency. Days later, he dissolved Parliament, in which the African Party for the Independence of Guinea and Cape Verde had held the majority.

Before his campaign, Mr. Embaló repeatedly said that even if he did not win, Mr. Pereira should not be allowed to run the nation. Mr. Dias had promised to restore the government that Mr. Embaló dissolved.