More than 800 people have been killed by Myanmar's security forces since a wave of protests broke out across the country after the military seized power in a coup in February, an activist group said.

Myanmar has been in turmoil since the army ousted Nobel Peace laureate Aung San Suu Kyi's elected government and detained her and officials of her National League for Democracy party.

The military has responded to protests by pro-democracy supporters in cities and towns with lethal force, while there has been an upsurge in fighting...