UN Secretary-General Antonio Guterres on Monday reiterated his call for an immediate, full and unconditional ceasefire in Ukraine as a first step toward a just, lasting and comprehensive peace.

In a statement on the occasion of the fourth anniversary of the start of the Ukraine crisis, which falls on February 24, the UN chief said the crisis "is a stain on our collective consciousness, and remains a threat to regional and international peace and security."

The longer the crisis lasts, the deadlier it becomes, with civilians bearing the brunt of it, he said.

Guterres noted that for peace to be just, "it must be in line with the UN Charter, international law and relevant United Nations resolutions, respecting Ukraine's independence, sovereignty and territorial integrity."

"The United Nations remains ready to contribute to all efforts towards this end," he said.