UN chief Antonio Guterres warns that deadlock in the organisation's Security Council on the wars in Gaza and Ukraine risks "fatally" undermining its authority, stressing the need for "serious reform". As one of five permanent members of the 15-member council, the United States -- Israel's biggest ally -- has a veto that it has wielded three times so far to bar the body from calling for an immediate ceasefire in the Palestinian Territory, while Russia has exercised its veto to prevent any action on the war in Ukraine.