The U.N Human Rights Officials said it has received credible information that on Sunday, at least 18 people were killed and 30 were wounded in a crackdown on anti-coup protesters in Myanmar.
They added that mass arrests were also made in the crackdown.
It would be the highest single-day death toll among the protesters who are demanding that Aung San Suu Kyi to be restored to power after being ousted by a February 1st coup.
On Sunday, about 1,000 people are believed to be detained.
The U.N Human Rights Office said in a statement that reportedly deaths occurred as a result of live ammunition fired on protesters in Yangon, Dawei, Mandalay, Myeik, Bago and Pokokku, adding that the forces used tear gas, flash-bang grenades and stun grenades.
U.N Human Rights Office spokesperson Ravina Shamdasani was quoted saying that we strongly condemn the escalating violence against protests in Myanmar and call on the military to immediately stop the use of force against peaceful protesters.
On Saturday morning, while providing news coverage of the protests, an Associated Press journalist Thein Zaw was arrested by the police and he remains in the police custody.
Phil Robertson, Deputy Asia director for New York-based Human Rights Watch said that the world is watching the actions taken by Myanmar military junta, and will hold them accountable. He also said that live ammunition should not be used to control or disperse protests and only lethal force can be used to protect life or prevent serious injury.
According to the Assistance Association of Political Prisoners, as of Saturday, 854 people had been arrested or charged in relation to the coup while 771 were being detained or sought for arrest. The group said that while it had documented 75 new arrests in several cities on Saturday.