An official from Aung San Suu Kyi’s party died in custody in Myanmar after being arrested during raids by security forces in Yangon.
On Sunday, the body of U Khin Maung Latt was released to his family, who were reportedly told he had died after fainting.
Photos show a blood-stained cloth around the 58-year-old’s head.
Activists say he was beaten while detained by police and soldiers, and was subjected to harsh interrogation.
Protests continue against last month’s coup despite a bloody breakdown.
The UN says more than 50 people have been killed since the military detained Suu Kyi, Myanmar’s democratically elected leader, on February 1.
Authorities have exhumed the body of a victim, 19-year-old Kyal Sin, and said she had not been killed by police when she was shot from behind.
Photos from the protests show that she had her head turned away from the police.
In another development, the military rulers asked neighboring India to return more police officers who had crossed the border and sought refuge after refusing to carry out orders.
How did U Khin Maung Latt die?
He actively fought for candidates for Mrs Suu Kyi’s National League for Democracy (NLD) in the recent parliamentary elections and was also known for his welfare work, reports Irawaddy.
He had been “violently beaten and kicked before being taken from his home” around 22:00 (15:30 GMT) on Saturday, according to witnesses quoted by the news committee.
On Sunday morning, his family was informed that he had died after “fainting”, and they collected his body from a military hospital.
U Tun Kyi, from the former political prison association, told the AFP news agency: “He was beaten and taken during a raid since last night and it looks like he underwent a hard interrogation.”
On Friday, an NLD local official in a village in the Magwe region, U Htway Naing, was reportedly hacked to death by military supporters.
In Yangon, police carried out other night attacks on Saturday.
UN Special Rapporteur Tom Andrews told the BBC that video from various parts of Myanmar showed security forces repeatedly firing on buildings as they arrested.
“And you can see them walking down the streets of Yangon and shooting up through the windows while people look down on the streets in horror,” he said.
“These are gangs. This is criminal activity. They are terrorizing these neighborhoods. So there is a compelling reason why the world is acting and that the world is acting now.”
Where are the latest protests taking place?
Security forces fired tear gas at the country’s second-largest city, Mandalay, on Sunday after thousands of protesters gathered.
Demonstrations were also held in half a dozen other cities, news reports in which police used force against protesters in Yangon, Lashio and Bagan.
In the southern city of Dawei, a protest leader was quoted as saying, “They kill people just like killing birds and chickens. What will we do if we do not rebel against them? We must rebel.”
Myanmar in profile
Myanmar, also known as Burma, became independent from Britain in 1948. For much of its modern history, it has been under military rule.
Restrictions began to loosen from 2010 onwards, leading to free elections in 2015 and the installation of a government led by veteran opposition leader Aung San Suu Kyi the following year.
In 2017, Myanmar’s army responded to attacks on police by Rohingya militants with a deadly demolition, driving more than half a million Rohingya Muslims across the border into Bangladesh in what the UN later called a “textbook example of ethnic cleansing”