UN Secretary-General Antonio Guterres is warning that Iran may be defying a UN call to halt ballistic missile development even as it complies with the nuclear deal with six world powers.<br/><br/>The UN chief says in a report to the Security Council that the United Nations is investigating Iran's possible transfer of ballistic missiles to Houthi Shiite rebels in Yemen that may have been used in launches aimed at Saudi Arabia on July 22 and November 4. <br/><br/>The report on implementation of a UN resolution that endorsed the July 2015 nuclear agreement was obtained by The Associated Press.<br/>'<br/>The US Mission to the United Nations said Ambassador Nikki Haley would hold a news conference today in Washington to highlight its findings as well as Iran's "destabilising activities in the West Asia region and elsewhere in the<br/>world."<br/>'<br/>In the report, Guterres stressed that the nuclear deal remains "the best way" to ensure the exclusively peaceful nature of Iran's nuclear program. <br/><br/>He said President Donald Trump's October 13 decision not to certify the agreement under US law created "considerable uncertainty" about its future. Guterres welcomed support for the treaty from its other parties –China, Russia, Britain, France and Germany, the European Union and numerous other countries.