The United States on Thursday imposed sanctions on Chinese and Emirati companies and a network of Iranian firms that help export Iran’s petrochemicals, a step likely aimed at raising pressure on Tehran to revive the 2015 Iran nuclear deal. “The United States is pursuing the path of meaningful diplomacy to achieve a mutual return to compliance with the Joint Comprehensive Plan of Action,” Under Secretary of the Treasury for Terrorism and Financial Intelligence Brian Nelson said in a statement, referring to the 2015 agreement. “Absent a deal, we will continue to use our sanctions authorities to …