"We found it was necessary to keep fighting [after the 15 May coup bid] so that we can push Nkurunziza to keep thinking about what he is doing and maybe just resign," Ngendakumana said in the interview broadcast late Sunday.
Ngendakumana, a top intelligence officer and ally of thwarted coup leader General Godefroid Niyombare, warned of new attacks.
"All those actions that are going on in the country, we are behind them and we are going to intensify them until Pierre Nkurunziza understands that we are there to make him understand by force that he has to give up his third term," he said.
The former general explained that 12 generals were in agreement about the coup until the defence minister alerted Nkurunziza who was in Dar Es Salaam for an East African Community summit.
“We were sure of success,” he said.
“He [the minister] negotiated money from the president,” the general alleged, blaming the minister for ordering loyalist troops to put down the insurrection.
Observers have greeted these allegations with scepticism.
“That’s a claim that’s almost impossible to validate,” noted a Bujumbura-based filmmaker, Pádraic MacOireachtaigh. “We’re very unsure about whether that could be the reason [for the coup’s failure] or whether in fact there was some incompetence behind the execution of the coup.”
The controversial interview went to air as Nkurunziza prepared to hit the campaign trail ahead of the presidential polls, due 15 July, and senatorial elections, scheduled for 24 July.
On Monday he spoke to thousands of supporters in Bugendana, the capital of Gitega province, in central Burundi.
The East African Community leaders asked Burundi on Monday to postpone the presidential election to 30 July.
But it’s unclear how much influence the EAC has on Nkurunziza, who did not attend Monday’s summit in Tanzania.
The ruling party at the weekend told United Nations mediator Abdoulaye Bathily to step down just two weeks after he was appointed "because he seriously lacked respect for the country's sovereignty," CNDD-FDD party spokesman Gelase-Daniel Ndabirabe told AFP.
Bathily, a Senegalese former minister, replaced mediator Said Djinnit, an Algerian diplomat, who stepped down after he was branded as pro-government by civil society activists.
Burundi’s tough-skinned president does not much care about foreign pressure, not even from the UN, which played a key role in the country’s stabilisation after the civil war, according to Benjamin Chemouni, a London School of Economics researcher.
“Nkurunziza really wants to legitimise his power through new elections and is not very sensitive to any type of leverage that the international community could put on him,” he explained in an interview. “His priority is the elections. Negotiations may come later.”
Nkurunziza's head of communications, Willy Nyamitwe, has been urging the international community, and particularly former colonial power Belgium, to respect the results of the polls.
"The elections in Burundi were a vote of the people, who are sovereign,” he said in Dar es Salaam at the weekend. “It is not for the Belgian people or government to dictate what the Burundian people should do."
The results of recent parliamentary polls have yet to be released but former colonial power Belgium has said it will not recognise the outcome.
Renegade general Ngendakumana, who has been on the run since the coup was thwarted, said that Niyombare, whose whereabouts are unknown, is still in Burundi.
“Ngendakumana claims he has now returned to Burundi where he is still receiving orders from Niyombare and that they are planning further action against the president,” explained MacOireachtaigh in a phone interview. “He said the only reason he had left Burundi was to give an interview to this Kenyan television station."
Follow Michel Arseneault on Twitter @miko75011