Prime Minister Patrice Trovoada said that overnight four men, including the former president of the outgoing National Assembly, tried to attack army headquarters.
One of them was a former military officer who attempted a coup in 2009, the prime minister said.
"We were targeted by an attempted coup, which began around 00:40 and was completed... shortly after 06:00," he said.
In the video footage authenticated and sent to AFP in Libreville by Sao Tome's justice minister, Trovoada is shown seated at a desk and says he wants to "reassure" the population and "the international community."
"There was an attempted coup d'etat which began around 00:40 am and... ended shortly after 6 am," he said, adding that "armed forces were attacked in a barracks."
Four attackers were "neutralized" and detained, and the National Assembly's ex-president Delfin Neves was arrested on Friday morning, Trovoada added.
"Everything indicates (that the coup occurred under) the command of some personalities", he added.
A former soldier, Arlecio Costa, has also been detained in relation to the coup.
The head of West Africa's main regional bloc ECOWAS, Guinea-Bissau President Umaro Sissoco Embalo, condemned the coup attempt on Friday.
"Sao Tome and Principe is a country considered a model of parliamentary democracy in Africa," he tweeted.
The former Portuguese colony, located off the western equatorial coast of central Africa, has been relatively stable since an attempted military coup against the government of President Fradique de Menezes in 2003.
Coup leaders at the time said they tried to topple the regime due to widespread poverty.
This report was compiled with data from Reuters and Agence France-Presse