United Nations – 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.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.The report on implementation of a UN resolution that endorsed the July 2015 nuclear agreement was obtained on Wednesday by The Associated Press. The US Mission to the United Nations said Ambassador Nikki Haley would hold a news conference on Thursday in Washington to highlight its findings as well as Iran's "destabilising activities in the Middle East region and elsewhere in the world".In the report, Guterres stressed that the nuclear deal remains "the best way" to ensure the exclusively peaceful nature of Iran's nuclear programme.ALSO READ: Iran tells France nuclear deal 'not negotiable'He said President Donald Trump's October 13 decision not to certify the agreement under US law created "considerable uncertainty" about its future. But, he added, "I am reassured that the United States has expressed its commitment to stay in the Joint Comprehensive Plan of Action for now".Trump, however, has left open the possibility of pulling out of the nuclear deal.Guterres welcomed support for the treaty from its other parties – China, Russia, Britain, France and Germany, the European Union and numerous other countries."I encourage the United States to maintain its commitments to the plan and to consider the broader implications for the region before taking any further steps," he said. "Similarly, I encourage the Islamic Republic of Iran to carefully consider the concerns raised by other participants in the plan."'Capable of delivering nuclear weapons'Trump has called the agreement a bad deal, and the US has focused especially on its time limits and a provision in the Security Council resolution that calls on Iran not to undertake any activity related to ballistic missiles designed to be capable of delivering nuclear weapons.Guterres said the UN is studying debris from missiles fired at Yanbu in Saudi Arabia on July 22 and at the capital of Riyadh on November 4 and also is reviewing other information.He said France, Germany, Britain and the United States sent a letter saying the Simorgh Space Launch Vehicle that Iran launched on July 27, if configured as a ballistic missile, is "inherently capable of delivering nuclear weapons".But Guterres said Russia, an ally of Iran, sent a letter on August 16 that the Security Council resolution contains only a "call" for Iran to forgo missile work – not a prohibition. He said Iran says the launch vehicle was "part of a scientific and technological activity related to the use of space technology" that it is determined to pursue.ALSO READ: Hollande slams Trump's 'double fault' over Iran nuclear dealThe Security Council discussed the launch on September 8, and "there was no consensus among council members" on how it related to the 2015 resolution, Guterres said.He said Israel protested that Iran's test of a Qiam ballistic missile on November 15, 2016 "used a Star of David as the intended target", and citied other ballistic missiles it reportedly launched at targets in Syria on June 18-19. France, Germany, Britain and the US also raised these tests as well as the test of a medium-range missile on July 4.The secretary-general said Iran called Israel's claim of a specifically marked target "a sheer falsehood".Iran also said its "military capabilities, including ballistic missiles, have not been designed to be capable of delivering nuclear weapons and thus are outside the purview of the Security Council resolution," Guterres said.