Myanmar security forces opened fire at a funeral on Sunday, witnesses said, as people across the country gathered to mourn 114 people killed the previous day in the worst crackdown on protests since last month’s military coup.

Mourners fled the shooting at a service for 20-year-old student Thae Maung Maung in Bago near the commercial capital Yangon and there were no immediate reports of casualties, three people in the town told Reuters...