Slovenian diplomat Janez Lenarcic, director of a human rights program at the Organization for Security and Cooperation in Europe, said the right to peacefully assemble shouldn't be jeopardized by disproportionate force.
"There can be no justification for physical assaults and violence against peaceful protesters," he said in a statement. "Any and all reports of the undue use of force against protesters must be promptly and thoroughly investigated."
Police most recently in Ukraine were accused of using force to quiet demonstrations over the government's decision to suspend efforts to sign free trade and association agreements with the European Union.
OSCE Secretary-General Lamberto Zannier said last week during a conference in Kiev member states, Ukraine being one of them, need to protect fundamental freedoms and respect the rule of law.
Governments in the Middle East and North Africa were accused of using a heavy hand during the wave of pro-democracy protests that gripped the region in 2011.
"Those suspected [of using disproportionate force] must be prosecuted and, if found guilty, they must be punished," the Slovenian diplomat said.
He was speaking on the occasion of International Human Rights Day.