DUBAI, United Arab Emirates — Iran closed its airspace to commercial flights for hours without explanation early Thursday as tensions remained high with the United States over Tehran’s bloody crackdown on nationwide protests . The closure ran for over four hours, according to pilot guidance issued by Iran, which lies on a key East-West flight route. International carriers diverted north and south around Iran, but after one extension, the closure appeared to have expired and several domestic flights were in the air just after 7 a.m. Iran previously shut its airspace during the 12-day war against Israel in June and when it exchanged fire with Israel during the Israel-Hamas war. However, there were no signs of current hostilities though the closure immediately rippled through global aviation because Iran is located on a key East-West route for airlines. “Several airlines have already reduced or suspended services, and most carriers are avoiding Iranian airspace,” said the website SafeAirspace, which provides information on conflict areas and air travel. “The situation may signal