DEAD SEA, Jordan - U.S. Secretary of State Colin Powell said Sunday he was concerned about the Israeli killing of a leading member of Hamas but nevertheless emphasized that Hamas and Islamic Jihad shoulder primary responsibility for the difficult situation facing the Palestinian people. Powell added that Middle East peace negotiators needed to keep working despite the killing of the Hamas leader in Hebron on Saturday at the hands of Israeli special police forces. "I regret we had an incident that could be an impediment to progress," he told a news conference after a meeting of the "Quartet" of key...