(OSV News) -- Two U.S. and two Japanese bishops have issued a joint letter to leaders of the Group of Seven (G7) nations, calling on them to take 'concrete steps' toward ending the use of nuclear weapons.The G7 leaders -- representing the U.S., Japan, Germany, the U.K., France, Canada and Italy -- are meeting May 19-21 in Hiroshima, Japan, the hometown of that nation's prime minister, Fumio Kishida.'We strongly urge world leaders at the G7 Summit to show by example how international leadership i