BEIRUT/CAIRO (Reuters) -U.S. officials believe Israel has narrowed down targets in its potential response to Iran's attack this month to military and energy infrastructure, NBC reported on Saturday. Tehran, a major oil producer, has threatened Israel with severe consequences if the Islamic Republic is attacked. Israel has repeatedly said it will respond to Iran's missile barrage on Oct. 1, which was launched in retaliation for Israel's military operations in Gaza and Lebanon and the killings of a string of Hamas and Hezbollah leaders.