Iran closed its airspace to commercial flights without explanation early Thursday as tensions remained high with the United States over Tehran’s bloody crackdown on nationwide protests.

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.

Iran in the past has misidentified a commercial aircraft as a hostile target. In 2020, Iranian air defense shot down Ukraine International Airlines Flight PS752 with two surface-to-air missiles, killing all 176 people on board. Iran for days adamantly dismissed allegations of downing the plane as Western propaganda before finally acknowledging it.