One week ago, Myanmar military forces warned pro-democracy protesters that if their demonstrations continued, there would be further loss of life.

The military has made good on its threat.

Sunday was the bloodiest day in Myanmar since a military junta seized power there one month ago. According to the United Nations Human Rights Office, at least 18 people were killed and more than 30 wounded after security forces fired live ammunition into crowds of peaceful demonstrators in several cities across the country.

“The people of Myanmar have the right to assemble peacefully and demand the restoration of democracy,” U.N. Human Rights Office spokesperson Ravina Shamdasani said in a statement. “These fundamental rights must be respected by the military and police, not met with violent and bloody repression. Use of lethal force against non-violent demonstrators is never justifiable under international human rights norms.”

In additional to live rounds, police also used tear gas to disperse thousands of protesters in major cities including Yangon, Dawei and Mandalay. Gruesome images widely shared on social media showed people running for cover as victims lay bleeding on the ground.

One of Sunday’s victims was Internet network engineer Nyi Nyi Aung Htet Naing. Reuters reports that one day earlier, he posted a question on Facebook: How many dead bodies before the United Nations takes action? The next day, he was one of five people killed in Yangon.

Another Yangon victim was killed after being shot in the eye. A middle school teacher reportedly died from a heart attack after a police stun grenade went off nearby.

In Mandalay, a man riding a motorbike was killed when a bullet pierced his helmet. A reporter on the front lines quoted one officer telling the crowd: “Get inside your homes if you don’t want to die,” Reuters reports.

In addition to using force on protesters, the military detained at least 85 medical personnel and students and seven journalists Sunday, the U.N. reported. Since the beginning of the coup on Feb. 1, more than 1,000 people have been “arbitrarily arrested,” the U.N. says — and some are still unaccounted for.

Meanwhile, state-run media said police were taking action in order to “protect the safety of people, the rule of law and community peace.” The government-run Global New Light of Myanmar reported that police are working to discover who is leading the protests, and will take “serious action” against them.

Aung San Suu Kyi, the civilian leader deposed by Myanmar’s military on Feb. 1, has not been seen since she was detained, the BBC reports. She is scheduled to appear in court Monday, but her lawyer says he hasn’t been able to speak with her.

On Friday, Myanmar’s ambassador to the U.N., who was appointed under the country’s civilian government before the coup, pleaded with the world to help. “We still need the strongest possible action from the international community to immediately end the military coup,” Kyaw Moe Tun said. He was removed from his position as ambassador the next day.