Nairobi (AFP) - A government commission which has exhumed the remains of more than 6,000 Burundians slaughtered in pogroms in 1972 is being accused of exploiting the sombre task for political gain and stoking ethnic tensions ahead of elections.

The Truth and Reconciliation Commission (TRC), set up in 2014 to deliver justice and closure to victims of Burundi's darkest chapters, has been excavating the mass grave since the start of the year -- and believes there are many more similar sites.

Hundreds of thousands of Burundians died in waves of ethnic violence and civil war that have scarred the country since independence in 1962, with massacres between the Hutu ethnic majority and the minority Tutsi.

Two major slaughters were the 1972 killings of mainly Hutu by Tutsi and the 1993 killings of mainly Tutsi by Hutu.

The TRC was established in 2014 to deliver justice and closure to victims of Burundi's darkest chapters.

On Monday, Commission chairman Pierre-Claver Ndayicariye said graves discovered along Ruvubu, about 20 kilometres (12 miles) from Burundi's new administrative capital Gitega, could be just the beginning.

"Witnesses speak of other mass graves further away in cornfields," he told AFP, indicating a dozen other sites had been flagged for investigation.

But opponents of Burundi's ruling party say the commission has abused its mandate by preferencing excavation work at sites where Hutus were buried, while ignoring pits containing Tutsi victims.

Critics allege the commission's work at Ruvubu amounts to political interference at a critical moment as presidential elections loom in May.

"The TRC is deliberately targeting mass graves which it says are those of Hutu victims, while every one knows there was a slaughter of Tutsi in 1993," near the current sites being explored, said Emmanuel Nkurunziza, from the Canadian branch of AC Genocide Cirimoso, an activist group.

"It is participating in the election campaign" of the ruling CNDD-FDD party by rallying Burundi's Hutus to its cause, he said.

Story continues

President Pierre Nkurunziza is a former Hutu rebel whose father was killed in one of the ethnic massacres in 1972 that decimated the Hutu elite.

The cultish leader, who believes he was chosen by God to rule the nation, is not seeking a new mandate after his contentious election to a third term in 2015 plunged Burundi into a crisis.

The violent aftermath left 1,200 people dead and made Burundi a focus of an investigation by the International Criminal Court for alleged murder, rape, torture and disappearances.

- 'They are Burundians' -

Despite the Hutu being the majority in the country, it was the Tutsi who were favoured by colonial administrators who held a monopoly on power after independence.

Burundi's first Hutu prime minister after independence was assassinated in 1965. That same year after the Hutu won a parliamentary election the then-king refused to accept their choice as prime minister and appointed a Tutsi.

It was these tensions which simmered and culminated in a Hutu revolt in 1972 in which thousands of Tutsi were killed, followed by a deadly reprisal which Hutu activists say led to between 100,000 and 300,000 of their people being massacred.

Witnesses told the commission that in May and June 1972, Hutus "were transported from Gitega prison by trucks every night" to the banks of the Ruvubu, where they were executed and dumped in pits.

Ndayicariye said "it was not for the commission to say whether the victims were Hutu or Tutsi".

"They are Burundians, first and foremost," he said, adding a thorough investigation would identify the victims and their tormentors.

But Vital Nshimirimana, a civil society activist in exile, said the commission had drawn "hasty conclusions" to support a narrative of Hutu victimhood, a potent rallying cry in the pre-election phase.

In 1993, the country's first free presidential election saw the first Hutu president elected. Just four months later the president was assassinated in an attempted Tutsi-led coup, setting off a wave of killings of thousands of Tutsi.

The events prompted further reprisals and plunged the country into a civil war which lasted until 2006 and left an estimated 300,000 dead on all sides.

As in neighbouring Rwanda, where similar ethnic tensions culminated in the 1994 genocide of at least 800,000 mainly Tutsi by Hutu, the historical narrative of victimhood remains extremely sensitive.

- 'No credibility' -

The TRC has so far identified 4,000 grave sites across the country and exhumed 142,500 victims.

The commission is comprised almost exclusively of ruling party cadres and Ndayicariye, its chairman, was head of Burundi's election commission during the 2010 and 2015 polls.

Nkurunziza won both in disputed circumstances -- the first unopposed when the opposition boycotted, and the second after sidestepping constitutional limits to run again.

"The current TRC has no credibility or independence," said Chauvineau Mugwengezo, the exiled Belgian president of the CFOR-Arusha, a collective of opposition parties.

The commission is stacked by ruling party hardliners and "is being used for electoral purposes, risking rekindling ethnic hatred in Burundi", he added.