Hussein Radjabu, the former boss of President Pierre Nkurunziza's CNDD-FDD ruling party, was arrested in April over the allegations of fomenting insurgency. Radjabu has denied the charges in the trial which began in December.

The public prosecutor said Evariste Kagabo, accused of being part of the plot, had been in charge of recruiting former fighters and distributing weapons. Kagabo denied the charges against him.

"I was beaten by intelligence officers, who forced me to accuse Hussein Radjabu of planning to overthrow the country," Kagabo told the court late on Wednesday. "They even promised to give me money, but I refused."

The tiny mountainous country of 8 million is emerging from more than a decade of civil war that killed over 300,000 people.

The prosecution said Radjabu had met 40 former fighters at his residence in the capital Bujumbura in March last year to organise an insurgency against the coffee-growing country's government.

Kagabo said he had not attended such a meeting.

Another suspect, Jean Marie Haragakiza, also said he was intimidated by the police to confess. The court is due to hear other suspects during this week.

Radjabu, was seen by many as the real power behind Nkurunziza with control over finances and the party's intelligence. He denied the charges on Tuesday in his first testimony since the trial began in December.

He was also blamed by some for corruption in the government and a trial against opposition politicians, including a former president, accused of a coup plot. That trial was seen as an orchestrated affair and ended in acquittal.