GENEVA (Reuters) - There has been an "alarming upsurge" in the number of killings and arrests in Burundi after the president was sworn in for a disputed third term in office, the U.N. High Commissioner for Human Rights said on Monday.

Burundi has been mired in turmoil and sporadic violence since President Pierre Nkurunziza announced his bid for another five-year term in April. He was sworn in on Aug. 20 after winning an election boycotted by his opponents.

The opposition said his decision to run again violated a peace deal that ended 12 years of civil war in 2005. Protests marred the run-up to voting. Since then, there have been a series of killings of officials, politicians and others.

"Almost every day, dead bodies are found lying on the streets of some of Bujumbura’s neighbourhoods," Zeid Ra’ad Al Hussein said, referring to an "alarming upsurge" in arrests, detentions and killings.

Residents in the capital Bujumbura report frequent shootings and blasts, particularly in areas where there were protests before the election.

Without anyone being held to account, the U.N. rights chief said in a statement: "There is an increasing risk that spiralling tit-for-tat violence will plunge the country back into its bloody past."
He said many victims appeared to have been killed by a bullet fired at close range and sometimes showed signs of torture. They were often found with hands tied behind their backs.

Since April, he said his office had registered 134 killings and hundreds of arbitrary arrests. He cited 704 arrests since the start of September, creating overcrowding in prisons.
There was no immediate comment from government officials.

Separately, an army spokesman said a senior army officer, Major Emmanuel Ndayikeza, deputy commander of the Muha military camp in Bujumbura, had fled on Saturday and would be formally declared a deserter if he did not return within eight days.

The move suggests further fractures in the army, formed from a patchwork of rebel groups and the military after the civil war. A failed coup attempt in May highlighted rifts.
Earlier this month, the president urged Burundi's military to remain united after a failed assassination attempt against the army chief.

 Reuters International