Malawi’s main opposition party, which has been lobbying to annul the result of the May presidential election, said Monday its headquarters were burnt to the ground in an arson attack.

The Malawi Congress Party (MCP) said the offices in the commercial capital Blantyre had been “bombed” on Sunday evening, though police said there was no confirmed cause of the fire.

Months of protests have erupted in usually stable Malawi since President Peter Mutharika won a second term in a disputed vote count.

Lazarus Chakwera, leader of the MCP, alleges he was robbed of victory by fraud after losing by a narrow margin.

Mutharika claimed the protests were aimed at unseating his government and has vowed to end them.

The MCP and the United Transformation Movement (UTM) party, which came third in the polls, have launched a legal battle against the ruling Democratic Progressive Party (DPP) and the electoral commission.

The next court hearing in the case is due on Monday.

Allegations of electoral fraud included that many result sheets were altered using typewriter correction fluid.