The U.N. chief and the presidents of Turkey and Ukraine discussed ways to end the war started by Russia and secure Europe's largest nuclear power station, which has come under shelling at the front lines.

U.N. Secretary-General Antonio Guterres told reporters after talks in Lviv, Ukraine, on Thursday that he was gravely concerned by circumstances at the Zaporizhzhia nuclear plant and called for military equipment and personnel to be withdrawn.

Turkish President Tayyip Erdogan said he, Guterres and Ukrainian President Volodymyr Zelenskyy discussed building on a recent positive atmosphere to revive peace negotiations with Russia that took place in Istanbul in March.