Four men have been executed in Equatorial Guinea, less than an hour after being convicted of attempting to assassinate the country's president. Rights groups, including Amnesty International, have condemned the executions and the way the trial was carried out.

The four men were executed on Saturday in Malabo, an hour after being sentenced to death by military tribunal. They were convicted of orchestrating an attack on Equatorial Guinea's presidential palace in February 2009. The attack was initially blamed on Nigerian militants.

State radio reported the executions of Jose Abeso Nsue, a former army captain and his deputy Manuel Ndong Anseme, as well as former government employees Alipio Ndong Asumu and Jacinto Michá Obiang. They were rendered from Benin, where they had been living in exile, to Malabo, and held secretly at the city's Black Beach prison.

The government only released information regarding their whereabouts on Saturday, when they had already been executed.

"We had information that while they were in prison they were tortured to extract a confession from them," said Marise Castro, an Amnesty International's researcher for Equatorial Guinea.

She said the men were executed with chilling speed, with no opportunity to appeal against their convictions.

"The sentence was read at between 3 and 3:30. The family of one of the executed men, Jose Abeho, went to the prison to see him as it was his wish to say goodbye to them, and by the time they got there at around 4, they had already been executed," added Castro.

She said swift executions used to be common in Equatorial Guinea. But this is the first case of detainees being put to death immediately following the end of a trial.

"The justice system is really a joke, the penal codes are very old and I think one of the problems is that the judiciary is not independent therefore they cannot implement the law," Castro said.

Amnesty International said physical conditions have improved inside the country's infamous Black Beach prison in recent years. But the treatment of prisoners, which often includes torture and punishments, has not.

"The Equatorial Guinea government must stop torture and must prosecute all those responsible for torture when it happens," stated Castro.

The rights group is calling for the government of Equatorial Guinea to put an end to forced confessions and unfair trials.