The prime minister of the tiny West African state of Sao Tome and Principe said "extrajudicial executions" occurred after the army thwarted a coup last month.
"We have had, from our point of view, an attempted coup d'etat. The armed forces stopped this attempt," Prime Minister Patrice Trovoada said during a visit to Portugal, the archipelago's former colonial power.
"After the end of the operation, some hours afterwards, there were what we think were extrajudicial executions, the execution of people who were key witnesses," he said in an interview published Wednesday by the Portuguese agency LUSA.
"At the very least, there was a failure in command. People placed under the responsibility of the armed forces cannot die -- they are in detention," he said.
After meeting Portuguese President Marcelo Rebelo de Sousa, Trovoada also said judicial investigators, who have requested help from Portugal, had been asked to produce a "preliminary report" on what happened by the end of the year.
The authorities have previously said four people were killed after military headquarters in the capital Sao Tome came under a gun attack on the night of November 24.
But images have circulated on social media purportedly showing several detainees being tortured by men in uniform.
The turbulent episode has rocked the reputation of Sao Tome, a nation off the coast of central West Africa, for stability since it gained independence in 1975.
'Acts of treason'
On November 25, Trovoada said four people had been arrested after a six-hour gun battle at military headquarters.
Two other people, described by those detained as the "sponsors" of the attempted coup, were later arrested, he said.
They were opposition leader Delfim Neves, who is the outgoing speaker of the National Assembly, and a former mercenary and opposition figure named Arlecio Costa.
But two days afterwards, the armed forces chief of staff said three of the detainees had died of injuries following an "explosion," as well as Costa, who had died after he "jumped from a vehicle".
Twelve soldiers who "took part" in the attempted coup had also been arrested, the chief of staff said.
Neves was released on bail on November 30 and later held a press conference in which he said the accusations against him were a "sham" aimed at destroying him.
"The accuser (the fourth detainee) was left alive to say that Delfim Neves was one of the ringleaders behind this plot," he charged.
Photos and videos have been circulating online, purportedly showing men in military uniform brutally interrogating and torturing three detainees. AFP has not been able to independently verify the images.
On December 1, the government ordered an investigation into allegations that soldiers committed "cruel, degrading and inhumane acts."
Armed forces chief Olinto Paquete also announced he was resigning, saying he could not "accept such atrocities and acts of treason that harm the homeland."