Discovering the origins of Covid-19 is a moral imperative and all hypotheses must be explored, the head of the World Health Organization said, in his strongest comments yet that the U.N. body remains committed to finding how the virus arose. 

A U.S. agency was reported by the Wall Street Journal to have assessed the pandemic had likely been caused by an unintended Chinese laboratory leak, raising pressure on the WHO to come up with answers. Beijing denies the assessment.