UNITED NATIONS -- Secretary-General Antonio Guterres is warning that Iran may be defying a U.N. call to halt ballistic missile development even as it complies with the nuclear deal with six world powers. The U.N. 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 Nov. 4.

The report is on implementation of a U.N. resolution that endorsed the July 2015 nuclear agreement. The U.S. Mission to the United Nations said Ambassador Nikki Haley would hold a news conference Thursday in Washington to highlight its findings as well as Iran's "destabilizing activities in the Middle East region and elsewhere in the world."

Haley has been a critic of the Iran deal and has traveled to meet with the international atomic energy watchdog to make the case that Iran has violated both the letter and spirit of the accord with its ongoing support of terror groups, and for its ballistic missile development and sales, CBS News' Pamela Falk reports.

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In the report, Guterres stressed that the nuclear deal remains "the best way" to ensure the exclusively peaceful nature of Iran's nuclear program.

He said President Donald Trump's Oct. 13 decision not to certify the agreement under U.S. 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."

Mr. Trump, however, has left open the possibility of pulling out of the nuclear deal.

The report also refers to its review of "the emerging information on the possible transfer by the Islamic Republic of Iran of ballistic missiles…to the Houthis in Yemen which may have been used in the ballistic missile launches aimed at the territory of the Kingdom of Saudi Arabia." Instead of releasing its findings, the report suggests that the Council called a joint meeting of the Security Council Committee to be jointly briefed by the panel of experts on Iran, according to Falk.

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."

Mr. Trump has called the agreement a bad deal, and the U.S. 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 U.N. is studying debris from missiles fired at Yanbu in Saudi Arabia on July 22 and at the capital of Riyadh on Nov. 4 and also is reviewing other information.

He said France, Germany, Britain and the U.S. 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 Aug. 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.

The Security Council discussed the launch on Sept. 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 Nov. 15, 2016 "used a Star of David as the intended target," and cited other ballistic missiles it reportedly launched at targets in Syria on June 18-19. France, Germany, Britain and the U.S. also raised these tests as well as the test of a medium-range missile 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.