The United States is considering sanctions against a businessman in the United Arab Emirates and a network of companies suspected of assisting Iran’s oil exports, as part of a broader effort to increase diplomatic pressure on Tehran as US officials work to reach an agreement on Iran’s nuclear programme. According to corporate documents reviewed by The Wall Street Journal, shipping data, and people familiar with the matter, the firms and individuals under investigation have been using ship-to-ship transfers of oil in waters between Iraq and Iran and then forging documents to conceal the origin of the cargo. Those engaged can circumvent Western sanctions targeting Iranian oil by passing off the mixed oil as Iraqi.