At least 149 people have been killed in Myanmar since security forces cracked down on peaceful protesters, the Office for the United Nations High Commissioner for Human Rights said.
Myanmar has been rocked by political unrest and mass protests since the military seized control of the country on Feb. 1 and ousted the elected government of Aung San Suu Kyi.
At least 11 were killed on Monday and 57 were killed over the weekend, the UN said.
More than 2,084 people remained arbitrarily detained and at least five people have died in custody in recent weeks. At least two bodies have shown signs of severe physical abuse, indicating they were tortured, the UN said.
"There are many more reports of further killings that we have been not been able to corroborate yet," UN spokesperson Ravina Shamdasani said in a statement. "We are deeply disturbed that the crackdown continues to intensify, and we again call on the military to stop killing and detaining protestors."
On Monday, Myanmar's ruling military junta declared martial law in and around Yangon, the country's largest city, and in Mandalay, the second-biggest city, in response to the unrest triggered by last month's military takeover.
But protesters have continued to take to the streets and challenge the government takeover, led by coup leader Gen. Min Aung Hlaing.
Shamdasani said confirming information has become increasingly difficult due to the martial law and because neighborhoods where people have been killed and displaced have been cut off through state-imposed communication blackouts.
The coup reversed years of slow progress toward democracy in Myanmar. For five decades the country operated under strict military rule that led to international isolation and sanctions.
Suu Kyi's National League for Democracy party led a return to civilian rule with a landslide election victory in 2015. Her government would have been installed for a second five-year term last month but she and her party members were placed in military detention.
The Biden administration on Friday announced it was offering temporary legal residency to people from Myanmar due to the military takeover and the deadly force against civilians.
ABC News' Christine Theodorou contributed to this report