The prisoners appear to be the hundreds of students detained in early March while demonstrating against the February 1 coup that ousted the elected government of Aung San Suu Kyi.
In Myanmar's hinterland, army uproots ethnic Karen villagers
"We will never give up to an unjust military but we will carve our future together with our united power," Mahn Win Khaing Than, who was named the acting vice president by Myanmar's ousted lawmakers, said on Saturday.
Aung San Suu Kyi was arrested during the February 1 coup. This is the fifth offence she has been charged with since then.
The demonstrators used water, blankets and fire extinguishers to try to smother the smoking canisters but were eventually forced to give ground and disperse.
The escalation of violence in Myanmar as authorities crack down on protests against the February 1 coup is raising pressure for more sanctions against the junta.
Security forces in Myanmar escalated their crackdown on protests against last month’s military coup, with at least 38 people killed on Wednesday.
"We will continue to fight for a government which is of the people, by the people, for the people,'' Ambassador Kyaw Moe Tun told the UN General Assembly in a surprise speech on Friday.
About 3,000 teachers and students stood their ground a short distance from the barricades and barbed wire as the police watched impassively, holding riot shields and cradling rifles.
The military junta warned it was prepared to use lethal force against rallies inciting "riot and anarchy".