Jul 15 - A security threat is being blamed for halting what would have been the highest-level diplomatic visit since Hamas seized control. Hamas says its security forces had taken measures to ensure the safety of Middle East envoy Tony Blair and is blaming Israel for the cancellation even though he was not due to meet any leaders of the Islamist group. An Israeli diplomatic source said Blair was informed by the Israeli Defence Minister Ehud Barak "that there was a threat that could materialize as he entered the Gaza Strip." Paul Chapman reports.