The U.N. human rights office is calling for the release of Russians arrested for protesting President Vladimir Putin’s draft to build up Russia’s fighting capacity in Ukraine.

Nearly 2,400 demonstrators reportedly have been arrested in various locations across Russia following President Vladimir Putin’s declaration last Wednesday of a partial mobilization of troops to join the invasion of Ukraine.

His call up of 300,000 reservists to strengthen Russia’s battle-weary army in Ukraine has triggered mass anti-war protests. U.N. human rights spokeswoman Ravina Shamdasani says clashes have erupted between demonstrators and police in some instances, but most protests have been peaceful.

“While the majority of the protests are reported to have been peaceful, military and administrative buildings, including enlistment offices, have been attacked in several regions,” said Shamdasani. “We stress that arresting people solely for exercising their rights of peaceful assembly and freedom of expression constitutes an arbitrary deprivation of liberty.”

She says it is unclear how many people remain in detention.

Fear of being called up for service has sent thousands of people fleeing to other countries in hopes of avoiding the draft. Shamdasani says it is heartbreaking to see so many people resorting to such desperate measures in the context of what she calls an unnecessary war.

“What international human rights law does insist on is that where people wish to object to participation in hostilities or where they wish to declare a conscientious objection, this needs to be taken into account, this needs to be respected by the authorities.”

She says information needs to be provided to people who are hesitant about going to war, so they know how to raise a conscientious objection to participation.

Shamdasani notes there has been an acknowledgement on the part of Russian authorities that, in some cases, people have been asked to mobilize by mistake. She says she believes a hot line has been set up to deal with those cases.