A 20-year-old woman became the first anti-coup protester to die after she was shot in the head last week.
Mya Thwe Thwe Khaing was injured two days before her 20th birthday when police tried to disperse protesters.
An image of the protester being cradled after she was shot was widely shared, and her death has triggered further anger against the authorities.
The police have denied using lethal force at the rally in the capital Nay Pyi Taw on 9 February, but doctors have said two other protesters were also struck by live rounds.
“I want to encourage all the citizens to join the protests until we can get rid of this system,” her sister, Mya Tha Toe Nwe, told reporters. “That’s all I want to say.”
Authorities said they would investigate the case.
Mya Thwe Thwe Khaing was a supermarket worker who took part in protests following a military coup which overthrew Aung San Suu Kyi’s elected government.
On February 9 Mya Thwe Thwe Khaing travelled to the protest with her sisters from Yezin, a village north-east of the capital. The mass protest saw police use water cannons against protesters who refused to retreat. Her brother had begged her not to join the demonstrations out of fear that the police would use force and start shooting.
Video of the moment she was shot appeared to show her standing some distance from the police. She was placed on life support when she was taken to hospital and remained there until she died.
“We will look for justice and move forward,” a doctor told AFP news agency, adding that staff had faced immense pressure since she was taken to their intensive care unit.
Mya Thwe Thwe Khaing’s family are all supporters of Ms Suu Kyi’s National League for Democracy (NLD). Her brother said she voted for the first time in last November’s general election, which the NLD won by a landslide.
“We are heartbroken and cannot talk about it much now,” he told AFP on Friday.