Burundi was plunged into crisis when President Pierre Nkurunziza announced a controversial bid for a third term in April, leading to deadly street protests and an attempted coup in mid-May, which laid bare political splits within the military.

Coup leader General Godefroid Niyombare is now on the run, Defence Minister Cyrille Ndayirukiye has been arrested and hundreds of other alleged coup plotters are absconding or in jail.

Officers now fear the army is being purged along ethnic lines.

"I cannot sleep, I cannot eat, I almost fled the country several times," said one senior officer, speaking on condition of anonymity, adding that he has twice evaded arrest.

The officer is a former member of the pre-civil war army, the FAB, which was dominated by ethnic Tutsis and pitted against a host of Hutu rebel groups in the 1993-2006 civil war.

Officers are worried that Tutsi ex-FAB members are now being specifically purged, targeted on the pretext that they were complicit in the attempted putsch.

"No soldier of the former FAB, from private to general, feels safe," said the officer, despite the fact that both Hutus and Tutsis are among the alleged coup plotters on the run or in jail.

Coup leader Niyombare -- who relatives and intelligence sources say has sought refuge elsewhere in the region -- is a Hutu, who fought alongside President Nkurunziza in the CNDD-FDD Hutu rebel group that is now the ruling party.

About 150 members of the 11th Battalion, accused of spearheading May's coup attempt, are in jail but sources say that perhaps 300 others from the same unit have absconded with their weapons.

For two weeks, arrests have been increasing, with most of those detained former FAB soldiers, among them two colonels, a major and a captain, according to the Association for the Protection of Prisoners and Detainees, which said other officers had gone missing.

"We, the former FAB, are the only ones targeted, while those from the CNDD-FDD are not worried," said another officer, referring to the president's party.

- 'Destroying integration' -

The ethnic parity of the army -- made up of equal numbers of Hutu and Tutsi in a country where the population is 85 percent Hutu -- is considered a fundamental achievement of peace and a guarantee of stability.

The wounds inflicted on the army by the political crisis will be slow to heal and the consequences for Burundi could be explosive.

Army spokesman Gaspard Baratuza insisted that "only those who are suspected of involvement in the attempted coup are arrested".

But an outside analyst dismissed the claim with a stark warning over the growing divisions.

"The regime is destroying one of Nkurunziza's greatest achievements since taking office: the integration of former Hutu rebels and Tutsi ex-soldiers," the unnamed analyst said.

Former defence minister Pontien Gaciyubwenge, an ex-FAB Tutsi general, proclaimed his neutrality during the coup and was sacked soon afterwards, and then fled abroad.

His chief of staff Prime Niyongabo, a former Hutu rebel of the CNDD-FDD, had urged him to join the side of the police in opposing the coup and the anti-third term protests.

Nearly 40 people have been killed in demonstrations in the capital Bujumbura since Nkurunziza announced his bid for a third term -- but another officer warned things could get far worse if tensions in the army were not resolved.

"The day they really divide the army, it will not be like these protests we have experienced," the officer said.

"That will be the end of Burundi as a nation."