The military, which on Friday thwarted a coup bid in the tiny Portuguese-speaking archipelago off central Africa considered a beacon of democracy, announced "four human lives were lost" after "exchanges of fire" at a military site.

Prime Minister Patrice Trovoada told STP-Press that "four citizens" and 12 soldiers and fighters from South Africa's officially disbanded Buffalo Battalion were involved in the attempted overnight putsch.

The army on Sunday said 12 serving soldiers were involved.

They were "neutralised and captured" after trying to storm military sites and three of them died from their wounds despite the army's efforts to preserve their lives by taking them to hospital, Trovoada added.

One of the victims was Arlecio Costa, who once served as a mercenary in apartheid South Africa's Buffalo Battalion, disbanded in 1993. Trovoada accused him of being one of the ringleaders.

The army said Costa -- also held in 2009 over accusations of plotting a coup -- died following his arrest on Friday after he "jumped from a vehicle", without giving further details.

Trovoada said the former president of the outgoing National Assembly Delfim Neves was also one of several people arrested after the attack on army headquarters, in a Friday video message confirmed by the justice minister.

A judicial source told AFP two inquiries had been launched to investigate the alleged attack on a military barracks in Sao Tome and the "torture" and "murder" of four suspects.

- 'Subversion' -

The government on Sunday condemned what it called a "violent attempt to subvert the constitutional order", saying the deaths and the coup attempt would be investigated.

It added that an international team was coming to the archipelago to support investigators and called on the hospital services to look after the victims' bodies.

A resident speaking to AFP anonymously by phone said she had heard "automatic and heavy weapons fire, as well as explosions, for two hours inside the army headquarters" in the nation's capital.

In the video message, authenticated and sent to AFP by the press office of Sao Tome's prime minister, Trovoada is seen sitting at a desk saying he wants to "reassure" the population and "the international community".

Trovoada initially said a soldier had been "taken hostage" and wounded but "would be able to resume his activities in a few days".

A former Portuguese colony in the Gulf of Guinea, the nation of some 215,000 people is deeply poor and depends on international aid, but is also praised for its political stability and parliamentary democracy.