Myanmar's military fired on protesters on Sunday, killing at least 18, the deadliest day since the anti-coup protests started this month.
According to the UN Human Rights office, deaths were reported in several cities, including Yangon, Dawei and Mandalay, as law enforcement used live rounds and tear gas on unarmed protesters.
Ever since the country's leader Aung San Suu Kyi, and other cabinet members were overthrown and detained by the military on February 1, there have been constant protests by the people.
Hundreds of thousands, including government workers, gathered on the streets last week to protest against the military.
Social media footage showed protesters running away as security forces carrying live ammunition charged at them, and several people were taken away covered in blood.
The police crackdown, which started on Saturday, was expanded on Sunday as coup leaders attempted to end protests by civilians asking for their duly elected leaders' release.
According to reports, despite the gunshots, civilians didn't seem deterred. They had set up roadblocks and homemade shields in an attempt to take on the security forces.
As the tension increased, many more protesters arrived, sitting down on the road and chanting.
The United Nations Human Rights Office condemned the violence against protesters, saying it had "credible information" that at least 18 people had been killed on Sunday.
"The people of Myanmar have the right to assemble peacefully and demand the restoration of democracy," spokesperson Ravina Shamdasani said.
"Use of lethal force against non-violent demonstrators is never justifiable under international human rights norms."
According to local reports, at least four people were killed in Yangon's largest city, as police fired bullets, stun grenades, and tear gas.
The protesters remained defiant. "If they push us, we'll rise. If they attack us, we'll defend. We'll never kneel to the military boots," Nyan Win Shein told Reuters.
Another protester, Amy Kyaw, told AFP: "Police started shooting just as we arrived. They didn't say a word of warning. Some got injured and some teachers are still hiding in neighbours' houses."
In the south-eastern city of Dawei, security forces moved to break up a rally. There are also reports of live rounds being used in that city, with four reportedly killed. In another large rally in Mandalay, police used water cannons and fired into the air, killing one person.
The UN said deaths had also been reported in Myeik, Bago and Pokokku.
The number of arrests since the protests began has not been confirmed. The Assistance Association for Political Prisoners monitoring group has put the figure at 850, but hundreds more appear to have been detained this weekend.
Aung San Suu Kyi, Myanmar's civilian leader, has not been seen in public since she was arrested and detained by the military junta in the capital Nay Pyi Taw.