The world’s largest group of oil-tanker underwriters is in talks with the U.S. government to find a way to insure Iranian petroleum shipments now that sanctions over Iran’s nuclear program have ended, the organization’s chief said Monday. The U.S. maintains several layers of sanctions against Iran, including a ban on dollar transactions, that undermine insurers’ ability to offer effective coverage for Iranian oil shipments to Europe, said Andrew Bardot, the executive officer of the London-based International Group…