That's according to a statement posted on the website of the Organization for Security and Cooperation in Europe, Ukrinform reports.
"Today we mark one year since the people of Ukraine were forced to stand strong against Russia's illegal, unjustifiable and unprovoked war of aggression in their country. Their resilience and courage in the face of unimaginable and senseless destruction is deeply inspiring," the statement said.
It added that this war is a threat to European and global security and stability. "It is an enormous human tragedy. It is crucial to ensure accountability for violations and abuses of human rights and international humanitarian law. Russia must be held accountable for all violations of international law," the OSCE leaders said.
They emphasized that it is necessary to ensure that "there is no impunity for international crimes committed in and against Ukraine, including for war crimes and the crime of aggression committed in Ukraine" and "its perpetrators should be prosecuted before the appropriate court."
"Our message today is clear: Russia's aggression must stop. Russia must end its violations of international law as well as of the principles and commitments of the OSCE," the OSCE leaders said.
They reaffirmed that they stand by Ukraine in its time of need and fully support "its sovereignty and territorial integrity within its internationally recognized borders and recognize its inherent right to self-defense."
"We reiterate our demand for Russia to immediately stop its war and fully and unconditionally withdraw from Ukraine," the statement said.