The U.S. and Britain on Sunday urged Israel not to attack Iran's nuclear program as the White House's national security adviser arrived in the region, reflecting growing international jitters that the Israelis are poised to strike. In their warnings, both the U.S. joint chiefs of staff, Gen. Martin Dempsey, and British Foreign Minister William Hague said an Israeli attack on Iran would have grave consequences for the entire region and urged Israel to give international sanctions against Iran more time to work. Dempsey said an Israeli attack is "not prudent," and Hague said it would not be "a wise thing."