Student-led rallies calling for education reform have twice been brutally suppressed in Myanmar in recent days.
In chaotic scenes on March 10, police armed with batons lashed out at students and activists in the central town of Letpadan, arresting 127 people and carting them off to prison by the truckload.
"We are concerned about the arrest of more than 100 students and other protestors following their participation in demonstrations in Letpadan," on Tuesday, said Ms Ravina Shamdasani, spokeswoman for the UN human rights office.
While a number of the protesters were later released, around 60 of them were charged under various laws, she said.
"We urge the government to unconditionally release all those detained for the exercise of their rights to peaceful assembly and freedom of expression and to amend the laws that place unnecessary and disproportionate restrictions on people's rights," Ms Shamdasani said.
In particular, the UN agency called for a revision of Myanmar's law on the Right to Peaceful Assembly and Peaceful Procession, under which many of the protesters were charged.
Ms Shamdasani also expressed concern over reports that "police used excessive and disproportionate force against the protestors."
While noting that the government had launched an investigation into another incident in Yangon on March 5, the UN rights office urged it "to also investigate the handling of Tuesday’s protests."
"Any use of force by the authorities may only be exercised in a manner that it strictly necessary and proportional to the seriousness of the offence," Ms Shamdasani said.
Students have rallied in Myanmar for months against education legislation, calling for changes to a new law, including decentralising the school system, allowing student unions and teaching ethnic minority languages.
The students have been marching to Yangon from central Myanmar's Mandalay Region since 20 January in their bid to alter the education law.
Talks between the government and the young activists had led to a rethink of the legislation by parliament, which is currently debating proposed changes.
But students pulled out of the discussions last week because of police efforts to stop the Letpadan activists from going to Yangon.