Open this photo in gallery:An Iranian passenger leaves Najaf International Airport after arriving on an AVA Airlines flight, in Najaf, Iraq, on Wednesday.Alaa Al-Marjani/ReutersSave for laterIranian flights to Gulf neighbours including travel hub Dubai appeared to have been cancelled on Thursday after a U.S. deadline passed for global firms to halt work with Iran’s airlines, a major step in a campaign President Donald Trump calls “economic D-Day.”In Saudi Arabia, where an escalating conflict with Yemen’s Iran-aligned Houthi fighters this month has become the main front in the wider Middle East war, authorities said they had intercepted six ballistic missiles fired...