Pope Leo made an urgent plea Thursday for global leaders to end world hunger, saying in a speech to a United Nations agency that allowing millions to go without food each day represented "an ethical derailment."

In a visit to the Food and Agriculture Organization (FAO) headquarters in Rome, the Catholic pontiff also condemned the use of hunger as a weapon of war, without naming any specific conflicts or nations.

Leo cited U.N. figures that around 673 million people do not eat enough each day, calling that number "the clear sign of a prevailing insensitivity, of a soulless economy... and of an unjust and unsustainable system of resource distribution."

"In a time when science has lengthened life expectancy … allowing millions of human beings to live – and die – struck by hunger is a collective failure, an ethical derailment, an historic offense," said the pope. Leo, the first U.S. pope, spent much of his career before the papacy as a missionary in Peru and has made caring for the poor an early focus of his five-month tenure.

He spoke Thursday to some 125 delegations attending a week-long forum coinciding with FAO's 80th anniversary.

The pope, speaking mainly in Spanish, said that today's conflicts "have seen the re-emergence of the use of food as a weapon of war."

"International humanitarian law, without exception, prohibits attacks on civilians and on goods essential to the survival of populations," he said.

"This seems forgotten, for, painfully, we witness the continued use of that cruel strategy," said the pope. "We cannot continue like this, since hunger is not humanity's destiny but its downfall."