Activists in Myanmar say at least 89 people including children have been killed by security forces who shot at people defying warnings to stay at home on Armed Forces Day. 

The Assistance Association for Political Prisoners group said it was the deadliest day since protests in the country began in February. 

The government had issued a stark warning that anyone who took to the streets risked being shot "in the head and back."

At least four people were killed in the capital Yangon, and more deaths were reported in the second-largest city Mandalay. 

Leader Min Aung Hlaing addressed the nation to say his forces were protecting democracy. "The army seeks to join hands with the entire nation to safeguard democracy," he said. "Violent acts that affect stability and security in order to make demands are inappropriate."

It takes the number of civilians killed since the military takeover on February 1 to more than 400.