DUBAI, United Arab Emirates — Iran’s Supreme Leader Ayatollah Ali Khamenei has been transferred to a secure location inside the country with heightened security measures in place, two regional officials briefed by Tehran tell Reuters. The sources say Iran was in constant contact with Lebanon’s Hezbollah and other regional proxy groups to determine the next step after Israel announced that it had killed Hezbollah chief Hassan Nasrallah in a strike in south Beirut on Friday.