Nations including Germany and the U.S. jointly decried the military violence which resulted in over 100 deaths in one day.
The statement was issued by the defence chiefs of Australia, Canada, Germany, Greece, Italy, Japan, Denmark, the Netherlands, New Zealand, South Korea, the United Kingdom and the United States.
"Junta forces shot machine guns into residential areas, resulting in many civilians, including six children between ten and sixteen years old, killed", AAPP said.
The military government further escalated the use of deadly force Saturday with fighter jets launching air strikes in an area near the Thai border controlled by an armed ethnic group dedicated to overturning the coup, according toReuters.
After the bloodiest day since last month's military coup with 114 deaths last Saturday, security forces opened fire at a funeral on Sunday, witnesses said.
Earlier this month, the 66-year-old Trinamool Congress chief was injured; she said was pushed by four or five people against her vehicle and had the door shut on her at a time when there was no police personnel around her.
European Union foreign policy chief Josep Borrell said the junta's celebration of its armed forces had been blighted by "a day of horror and of shame".
The killings happened throughout the country as Myanmar's military celebrated the annual Armed Forces Day holiday with a parade in the country's capital, Naypyitaw.
They added that "the global community has a responsibility to protect the people of Myanmar from atrocity crimes".
Another 13 people were killed in other incidents over the weekend, according to the Assistance Association for Political Prisoners advocacy group on Sunday, taking its total toll of civilians killed since the Feb 1 coup to 459. The coup triggered mass protests which were met by the Junta's deadly violence.
Mourners were expected to turn out for funeral processions across the country Sunday, after the bloodiest day since the putsch.
"The people are anxious about whether the air strikes would come again today", she told AFP.
Despite the dangers, protesters hit the streets again on Sunday in parts of commercial hub Yangon and several other cities around Myanmar.
The UN put Saturday's death toll at 107 people - including seven children - but expected it to rise further.
"The shameful, cowardly, brutal actions of the military and police - who have been filmed shooting at protesters as they flee, and who have not even spared young children - must be halted immediately", United Nations envoys Alice Wairimu Nderitu and Michelle Bachelet said in a joint statement.
The General Strike Committee of Nationalities (GSCN), one of the main protest groups, in an open letter posted on Facebook urged armed ethnic groups "to collectively protect the people, youths, women, children and elders" who opposed military rule.
Henrietta Fore, head of the United Nations children's agency UNICEF, said in Saturday's bloodiest day since the coup "an 11-year-old boy, an 11-year-old girl, two 13-year-old boys, a 13-year-old girl, three 16-year-old boys and two 17-year-old boys, (were) all reportedly shot and killed".
The assault targeted the Fifth Brigade of the Karen National Union (KNU), one of the country's largest armed groups, which says it represents the ethnic Karen people.
But he also issued a threat to the anti-coup movement, warning that acts of "terrorism which can be harmful to state tranquillity and security" were unacceptable.
Later that evening, he entertained dignitaries including Russian deputy defence minister Alexander Fomin at a lavish outdoor dinner.
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