A group of military officers in Guinea-Bissau have claimed “total control” of the country, a day after the top candidates in a tightly contested presidential election both declared victory.

The officers released a statement on Wednesday, declaring that they had ordered the immediate suspension of the electoral process; the closure of all land, air and sea borders, and an overnight curfew “until further notice”.

The move came shortly after sustained gunfire was heard near the election commission headquarters, the presidential palace and the interior ministry in the capital, Bissau.

The results of Sunday’s presidential vote were expected to be announced on Thursday in the West African nation. The vote had pit incumbent President Umaro Sissoco Embalo against his primary challenger Fernando Dias.

Reporting from neighbouring Senegal on Wednesday, Al Jazeera’s Nicolas Haque said Embalo’s whereabouts were not immediately clear after the military officers’ statement.

“The presidential palace is heavily guarded as we speak, surrounded by the presidential guard, and we have the military deployed,” Haque said.

“What we know for sure is that the military is definitely in charge of the country today.”

Guinea-Bissau has experienced several attempted coups since it gained independence from Portugal in 1974.

Haque noted that the legitimacy of this week’s election was called into question by civil society groups and other observers after the main opposition party, the African Party for the Independence of Guinea and Cape Verde (PAIGC), was barred from running a presidential candidate.

“There’s been a clampdown of opposition candidates,” he said.