A man being interrogated by police in Burma detonated a bomb, killing himself and wounding four officers in eastern Karenni state, residents and officials said Wednesday.

The bomb Tuesday was the latest in a series of explosions to hit the military-ruled nation in recent weeks, as the reclusive junta government prepares to hold the country’s first elections in 20 years.

“A man about 30 years old exploded the bomb and killed himself. Four police beside him were injured during the blast at the police station,” a resident of Loikaw town in Karenni state told AFP, requesting anonymity.

“We do not know how he exploded the bomb,” he said.

An official confirmed the blast and casualties in Loikaw, 400 kilometres (250 miles) from Burma’s economic hub Rangoon.

“He had been taken to the police station for questioning as a suspect. Nobody suspected he would do this,” the official said on condition of anonymity.

It was unclear exactly why he was taken for questioning and if he had intentionally committed suicide.

Also Tuesday, a series of grenade blasts hit a hydropower plant under construction in neighbouring Bago province, run by Burmese company Asia World Construction.

Another of the company’s projects, a controversial dam in Kachin state, was hit by a series of bombs blasts earlier this month, injuring one engineer.

Three other bombs on 15 April hit a water festival in Rangoon, in the city’s worst attack in five years. The official death toll from that attack has now risen to 10 people, with at least 170 wounded.

Authorities have arrested suspects in relation to the Rangoon blasts, officials said, but declined to give further details while investigations were ongoing.

Burma has been hit by several bomb blasts in recent years which the junta has blamed on armed exile groups or ethnic rebels.

The latest attacks come as the country prepares for polls, planned for the end of this year, which critics have dismissed as a sham due to the effective barring of opposition leader Aung San Suu Kyi as she is a serving prisoner.

The military has ruled Burma since 1962, partly justifying its grip on power by the need to fend off ethnic rebellions that have plagued remote border areas for decades.

Armed minorities in Karen and Shan states continue to fight the government along the country’s eastern border, alleging they are subject to neglect and mistreatment.