Rebeca Grynspan must secure nine votes in the 15-member Security Council and avoid a veto from any of the five permanent members in the race to become UN secretary-general. (EPA Images pic)

UNITED NATIONS: Costa Rica's former vice-president Rebeca Grynspan appeared Wednesday a frontrunner in the race for UN secretary-general as she led informal polling for a fourth time, according to a diplomatic source.

A total of seven candidates -- four women and three men -- are vying to succeed UN chief Antonio Guterres, of Portugal, who ends his second five-year term on Dec 31, 2026.

The selection process is fraught with uncertainty as a single veto from one of the five permanent members of the 15-member UN Security Council can block a potential nominee.