Demonstrators were already grieving over Mya Thwate Thwate Khaing, a 20-year-old woman who died Friday of a shot to the head sustained at a protest in Naypyitaw on February 9.
A man was killed in Myanmar on Saturday when police fired to disperse protesting opponents of a 1 February military coup in the second city of Mandalay, media and an ambulance service said.
But tension escalated quickly in Mandalay where police and soldiers were confronting striking shipyard workers and other protesters.
The incident came after rubber bullets were earlier fired at protesters in the city, injuring two of them, according to report.
On Friday, a hospital official confirmed her death at 11 am, and said her body will be examined by a board at 3 pm as "this is a case of injustice".
"Shooting at a peaceful protester with real bullets is such an unforgivable thing in our society", said a doctor who was part of the team that gave her initial treatment, responding to her death.
But she travelled to the protest with her sisters from Yezin, a village north-east of the capital.
Much of the country has been in open revolt since troops deposed civilian leader Aung San Suu Kyi on February 1, with disparate strands of Myanmar society uniting to protest against a return to military rule.
On her birthday last week, Mya Thwate Thwate Khaing's friends had taken flowers and food to a Buddhist temple to pray for her recovery. "Two are seriously injured", a medical aide to the doctors said.
A memorial for Mya Thwate Thwate Khaing, a teenager who was shot in the head.
The military has blamed protesters for instigating violence.
Dr. Wai Phyo Aung of the committee representing elected members of the Union Parliament from the National League for Democracy told The Irrawaddy: "We appreciate that the worldwide community is taking action against the military for its unlawful act". "Above all, there should be strong global condemnation and strong consequences against the Myanmar military", Human Rights Watch's Myanmar researcher Manny Maung wrote on Twitter.
The US, Britain and Canadian governments have imposed sanctions on the new military leaders, and they and other governments have called for Suu Kyi's administration to be restored.
The army seized back power after alleging fraud in November 8 elections that the NLD swept, detaining her and others.
But since its power grab, it has instated multiple internet shutdowns, blocked some social media sites, and arrested hundreds - often in the middle of the night.
A spokesman for the ruling military did not deny that Mya Thwet Thwet Khine had been shot by security forces, but said at a news conference this week that she was in a crowd that had thrown rocks at police and the case was under investigation.
Almost 550 people have been detained since the coup, according to the Assistance Association for Political Prisoners.
Among those targeted have been railway workers, civil servants and bank staff who have walked off their jobs as part of a civil disobedience campaign aimed at crippling the army's ability to govern.
One teacher at the scene said she saw dozens arrested in the scuffle, including two of her colleagues.
The EU also "reiterates its call on Myanmar's security forces to refrain from violence against demonstrators protesting against the overthrow of their legitimate government", she added.