The US on Friday urged Myanmar's military to refrain from violence and relinquish power after the first death in protests against the coup.
But tension escalated quickly in Mandalay where police and soldiers were confronting striking shipyard workers and other protesters.
Earlier Saturday, in the largest city Yangon, a rally was held in memory of the female student, Mya Thwet Thwet Khine, 20, who was shot in the head while participating in a February 9 demonstration.
Video from the day she was shot show her sheltering from water cannons and suddenly dropping to the ground after a bullet penetrated the motorcycle helmet she was wearing.
Ko Aung and the doctor said a second man was shot in the chest and died later of his wound.
Amnesty said it has verified the coordinates of the image, which shows an officer holding a "Myanmar-made BA-94 or BA-93 Uzi clone".
"As protests continue to grow, Myanmar security forces must cease carrying and using lethal weapons and must respect people's right to peacefully express their grievances", Joanne Mariner, director of crisis response for Amnesty International, said in an emailed statement.
"The military truck is just picking people up from the protest", she said.
Gunshots were fired, though it was initially unclear whether live ammunition or rubber bullets were used.
The military regime has so far weathered a chorus of global condemnation.
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Protesters hold a demonstration against the military coup outside the Russian Embassy in Yangon on February 20, 2021.
Since the shooting, Mya Thweh Thweh Khine has become a symbol of the protests, which have intensified over the past two weeks.
Much of the country has been in uproar since troops deposed State Counsellor Aung San Suu Kyi and here elected civilian government on Feb 1, with large street demonstrations in major cities and isolated villages alike.
Some 500 police and soldiers descended on the area near Yadanabon dock after dock workers joined the national civil disobedience movement, refusing to work until the military junta that seized power in a February 1 coup reinstates the democratically elected government.
On Saturday, protests continued in Yangon, the country's largest city, while people mourned her death with wreaths and photographs.
She is under house arrest, accused of possessing illegal walkie-talkies and violating the country's Natural Disaster Law.
On Thursday, the United Kingdom and Canada imposed sanctions on three generals from Myanmar's junta, British Foreign Secretary Dominic Raab announced. Than Hlaing. All were sanctioned for their responsibility in serious human rights violations by the military or the Myanmar police force, Raab said. A doctor confirmed her death Friday, adding that her body will be examined as it is a "case of injustice".
The US, Britain, Canada and New Zealand have announced limited sanctions, with a focus on military leaders, including banning travel and freezing assets.
European Union foreign affairs spokesperson Nabila Massrali expressed condolences to Mya Thwate Thwate Khaing's family and friends, calling on Myanmar's security forces to refrain from violence against those "protesting the overthrow of their legitimate government", according to the German Press Agency (DPA).