The United States has issued what could be its most forceful threat to date of a potential attack on Iran. Speaking at a public event in Jerusalem, the U.S. ambassador to Israel, Dan Shapiro, said the Obama administration has made preparations for military action. Shapiro said the United States would prefer a peaceful resolution to the standoff over Iran’s nuclear activities. But he added: “That doesn’t mean that the [military] option is not fully available. And not just available, but it’s ready. The necessary planning has been done to ensure that it’s ready.”