BEIRUT -- A Saudi-dominated political bloc on Wednesday formally designated Lebanon's Hezbollah militia a terrorist organization, a move that signals dangerously escalating tensions between regional rivals Saudi Arabia and Iran. The Gulf Cooperation Council's decision against the Iranian-allied group comes two weeks after Saudi Arabia canceled $4 billion aid package for strengthening Lebanese security services. Saudi Arabia and other GCC member states have advised their citizens to leave Lebanon. An announcement posted on the GCC website accused Hezbollah, a powerful Shiite Muslim movement, of unspecified hostile acts in the six states in the bloc: Saudi Arabia, the United Arab Emirates,...