Former Burundi defence minister Cyrille Ndayirukiye and four other defendants have pleaded guilty to involvement in a failed coup last May during a trial of 28 police and military figures, judicial sources said Tuesday.

Ndayirukiye, number two among the coup plotters, and two other army generals and two police commissioners cited the violent repression of anti-government protests to justify their attempted takeover of power.

"I could not remain with my arms crossed while the police were killing the population, while President Pierre Nkurunziza was playing football and while the troops... appeared indifferent," army general Ndayirukiye said during his first statement from the witness box on Monday, the sources said.

They face possible life imprisonment.

Burundi was plunged into crisis last April when Nkurunziza announced a controversial bid for a third term, triggering deadly street protests followed by an attempted coup, which laid bare political splits within the military.

Coup leader General Godefroid Niyombare is currently on the run.

READ: Burundi coup leaders arrested after General Niyombare admits failure

The opposition and rights groups say the president's quest for a third term — which he won in July elections — violated a constitutional two-term limit as well as a 2006 peace deal that ended a 13-year civil war.

Ndayirukiye told the Supreme Court he and his co-accused should not take all the blame for the abortive coup, alleging that army chief Prime Niyongabo "gave me the orders".

The trial of the 28 accused opened on December 14 in Gitega, some 100 kilometres (60 miles) from the capital Bujumbura.

The failure of their coup bid and re-election of Nkurunziza have not stopped the unrest in the central African country.

READ: 48 hours: Inside Burundi coup that could have been but never was

At least one person was killed and a dozen injured in a series of grenade attacks early Friday in Bujumbura, police and official sources said.

The violence put an end to three weeks of relative calm after a day of bloodshed in the capital on December 11, when 87 people were killed, according to an official tally — although UN sources estimate the toll was far higher.