NEW YORK, April 21 -- Four contenders are squaring up to succeed Antonio Guterres as leader of the United Nations, which faces unprecedented global instability, wars and its own crushing budget crisis.

Chile's Michelle Bachelet, Argentina's Rafael Grossi, Costa Rican Rebeca Grynspan, and Senegal's Macky Sall will each face grillings by 193 member states and NGOs for three hours today and tomorrow.

It is only the second time the UN has held a public Q&A, a format created in 2016 to boost transparency.

Ultimately the five permanent members of the UN's top body, the Security Council, hold the power, wielding vetoes over who leads the global organisation as its secretary-general.

US President Donald Trump's envoy to the Manhattan-based UN...