A series of grenade blasts hit a hydropower project in Burma on Tuesday, wounding four workers in the latest unrest in the military-ruled country, officials said.

The attacks occurred at the Thaukyegat hydropower plant under construction in Bago division, about 220 kilometres (137 miles) northeast of the country’s main city Rangoon, a local official told AFP.

“Four workers were injured during three grenade attacks at the Thaukyegat hydropower project site,” the official said, asking not to be named because he was not authorised to speak to the media.

The Burmese company behind the project, Asia World Construction, was also involved in a controversial dam project in Kachin state where there was 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 death toll from that attack has now risen to 10 people, with at least 170 people wounded.

Burmese authorities have arrested some suspects in their search for the perpetrators of those blasts, officials said, but they did not give any further detail as the investigation is still underway.

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 elections planned for this year, which critics have dismissed as a sham due to the effective barring of opposition leader Aung San Suu Kyi because 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.