Security forces are "aggressively increasing their use of lethal weapons against peaceful protesters," she said, adding that 57 people have been killed since the weekend and 11 citizens have been killed in the past 24 hours.
These figures, which include those killed during the violent crackdown on the outskirts of Yangon city, are "conservative" because they record only those deaths that have been confirmed.
The spokeswoman added that her office has received reports of over 2,000 arbitrary arrests, use of torture, and enforced disappearances. The United Nations has also received reports of the use of snipers against demonstrators but this has not yet been verified.
"At least five deaths in custody occurred in recent weeks, and at least two of the victims showed signs of severe abuse indicating they were tortured," she added.
Confirmation of the data is becoming increasingly complicated due to martial law and internet and other media blackouts. So far, the military junta has also revoked the licenses of five major media outlets and detained 37 journalists.
"We call once again on the military to stop the killings and arrests of protesters," the UN spokeswoman said.