"The death toll has soared over the past week in Myanmar, where security forces have been using lethal force increasingly aggressively against peaceful protesters," UN rights office spokeswoman Ravina Shamdasani told reporters.

In total, she said, the office had corroborated that a total of 149 people had died in the crackdown on protests since February 1, but stressed that the actual number was surely much higher.

According to the Assistance Association for Political Prisoners (AAPP), more than 180 people have been killed, including 74 on Sunday alone.

In addition to the killings, Shamdasani warned that security forces were continuing to arbitrarily arrest and detain people throughout the country, with at least 2,084 people currently being held.

"Deeply distressing reports of torture in custody have also emerged," she said.

The office had determined that "at least five deaths in custody have occurred in recent weeks," she said, adding that "at least two victims' bodies have shown signs of severe physical abuse indicating that they were tortured."

- 'Enforced disappearances' -

In addition, "hundreds of people who have been unlawfully detained remain unaccounted for and have not been acknowledged by the military authorities."

This, Shamdasani said, "amounts to enforced disappearances."

Her comment came after security forces escalated the use of lethal force against anti-coup protesters, despite international appeals for restraint.

Much of the country has been in uproar since the military ousted civilian leader Aung San Suu Kyi last month, with hundreds of thousands taking to the streets to demand a return to democracy.

Shamdasani voiced concern that the UN rights office was facing increasing difficulty confirming information on the ground, pointing to the imposition of martial law in a range of townships in and around Yangon and Mandalay.

In addition, many of the working-class neighbourhoods where people had been killed had been cut off through state-imposed communication blackouts.

A dramatic crackdown on the media in the country was also complicating getting hold of information, she said, pointing out that at least 37 journalists had been arrested, while five major Myanmar news outlets had seen their licences withdrawn.

The UN rights office said the death toll had risen sharply in recent days, with 11 deaths on Monday, 39 on Sunday and 18 on Saturday.

Shamdasani said the figures, surely an underestimate, included people killed in the Yangon township Hlaing Tharyar "during a violent crackdown... by security forces after unknown actors set fire to Chinese-operated or -invested factories."