An al Qaeda affiliate in Algeria closed a base earlier this month after an experiment with unconventional weapons went awry, a senior U.S. intelligence official said Monday. The official, who spoke on the condition he not be named because of the sensitive nature of the issue, said he could not confirm press reports that the accident killed at least 40 al Qaeda operatives, but he said the mishap led the militant group to shut down a base in the mountains of Tizi Ouzou province in eastern Algeria. He said authorities in the first week of January intercepted an urgent communication...