Burundi police killed four gunmen after a heavy exchange of fire, a police officer said on Monday, the latest in a series of violent incidents that raise concerns about a new insurgency in the coffee-producing nation.

The clash took place late on Sunday in the western province of Cibitoke, a former hotspot during the civil war that lasted more than a decade since 2004, close to neighbouring Democratic Republic of Congo (DRC).

We had information that there was a group of armed men who wanted to cross into DR Congo. A police patrol surprised them and opened fire on them, said Joseph Kinyata, police chief in Cibitoke.

Four were killed on the spot and another one was injured, he said, and four hand grenades were seized in the operation.

Burundi authorities suspect that former Forces for National Liberation (FNL) fighters have their rear base in the DRC and that FNL boss Agathon Rwasa could be hidden there.

Landlocked Burundi has enjoyed relative peace since the former Hutu hardline rebel FNL laid down their weapons and joined the government in 2009 after almost two decades of insurgency.

But attacks on civilians and soldiers have intensified since elections last year were widely boycotted by the opposition. Analysts say fighting between the security forces and former militia fighters risks blowing up into a full-scale rebellion.

Many people have been urging President Pierre Nkurunziza to start talks with opposition leaders who are in exile to prevent a return to civil war.

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