A State Department official told lawmakers Thursday he was unsure of the precise location of tons of low-enriched uranium shipped out of Iran on a Russian vessel as part of the landmark nuclear agreement. Ambassador Stephen Mull, the lead U.S. official overseeing the deal's implementation, said during testimony before the House Foreign Affairs Committee that the stockpile is a Russian custody issue. He said the U.S. is confident the material will be controlled properly. "We obviously have had many differences for many years with Russia," Mull said. "But one of the features of our relationship is pretty close cooperation and...