SITTWE, Myanmar — A human rights group said Myanmar government forces opened fire in June on crowds of ethnic Rohingya in a campaign of violence during recent sectarian strife, as a UN envoy visited the area Wednesday to investigate the unrest.

Human Rights Watch called for a strong international response to ‘‘atrocities’’ committed during fighting in June between Rakhine Buddhists and Muslim Rohingya. The violence in western Myanmar that left 78 people dead has subsided, but tens of thousands remain homeless.

The official spokesman for Rakhine state rejected the group’s criticism of the government’s response to the violence. Win Myaing saidthat allegations that government forces stood and watched as violence wracked the area were ‘‘absolutely untrue.’’

‘‘Security conditions obviously improved day by day when government forces were deployed to control the situation,’’ Win Myaing said.

The report coincided with a visit by UN human rights envoy Tomas Ojea Quintana to Rakhine state. His evaluation of the conflict is likely to be regarded as a yardstick for measuring the reforms undertaken by elected President Thein Sein after Myanmar ended decades of military rule.