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

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The violence put an end to three weeks of relative calm after Dec.11 attacks on three military bases which left 87 dead, according to an official tally — although UN sources estimate the toll was far higher.

“A grenade was thrown into a bar around 10:00pm” in the central district of Buyenzi, police spokesman Pierre Nkurikiye told AFP, saying that 10 people were injured in the attack.

An official source who did not give his name said one person had died. The source added the bar was a regular haunt of members of the ruling party.

Nkurikiye said three policemen were also hurt in two other attacks in the city, where residents reported hearing shots and grenade blasts for around an hour in the early hours of Friday.

He added police would tackle any upsurge in violence after last year saw a failed coup in May amid unrest which sparked fears of a return to civil war.

Tensions rose after President Pierre Nkurunziza said he was seeking a controversial third term, which he went on to win in July.

UN sources estimate last year’s unrest prompted some 200,000 people to leave the country.