Guterres made the remarks while reporting on the implementation of Security Council resolution 2231 on Friday.
Referring to the UN Security Council's July 20, 2015, move to endorse the Joint Comprehensive Plan of Action (JCPOA) which had been signed between Iran and the six world powers few days before the date the same year, the UN chief said the Council endorsed the Plan at the time and called upon all Member States, regional organizations and international organizations to support its implementation.
For the past five years, the Plan has been largely viewed by the international community as a testament to the efficacy of multilateralism, diplomacy and dialogue and success in nuclear non-proliferation, he added.
"I have consistently believed that the Plan is the best way to ensure a comprehensive, long-term and proper solution to the Iranian nuclear issue, as well as to contribute to regional and international peace and security.
"I note the continued commitment of its participants to preserve the Plan, and the importance of the Plan working for all, including by providing tangible economic benefits for the Iranian people.
"I have encouraged all States to support the Plan and believed that issues not directly related to the Plan should be addressed without prejudice to preserving the agreement and its accomplishments.
"I regret the steps taken by the United States since May 2018, when it withdrew from the Plan.
"The reimposition by the United States of all its national sanctions, which had been lifted or waived pursuant to the Plan, is contrary to the goals set out in the Plan and in resolution 2231 (2015)."
"Other steps taken by the United States to restrict activities allowed within the framework of the Plan may also impede the ability of the Islamic Republic of Iran and the other Member States to implement certain provisions of the Plan and of the resolution," the UN chief noted.
About Iran's measures to reduce commitments to the international deal after the first anniversary of the US withdrawal from the JCPOA in May, 2019, the UN chief said "I note that the Islamic Republic of Iran has stated that it wants to remain in the Plan and has emphasized that all of its measures since 1 July 2019 are reversible."
He further referred to the latest reports from the International Atomic Energy Agency (IAEA) which stated that "Iran has decreased its stockpile of heavy water" and "has stayed within the Plan limits."
"I also urge the Islamic Republic of Iran to carefully take into account and address the other concerns raised by other participants in the Plan and by other Member States in relation to resolution 2231 (2015)."
Speaking about the world situation in the pandemic, Guterres stressed that "the importance of initiatives in support of trade and economic relations with the Islamic Republic of Iran, especially during the current economic and health challenges posed by the coronavirus disease (COVID 19) pandemic."
He also underscored the "important contribution of other Member States to preserving the Plan and continue to encourage them to work effectively with the participants in the Plan towards creating the conditions necessary for their economic operators to engage in trade with the Islamic Republic of Iran in accordance with resolution 2231 (2015)."
Elsewhere, the chief talked of the June 2019 arms seizure by Australia and said "the photographic analysis indicates" that it was "not of Iranian manufacture."
Also about the assassination of the Iranian scientist, Mohsen Fakhrizadeh, the UN chief said "In a letter dated 27 November 2020, the Permanent Representative of the Islamic Republic of Iran informed me and the President of the Security Council that on “27 November 2020 in Absard city of Tehran province, Mr. Mohsen Fakhrizadeh, a prominent Iranian scientist, was assassinated in a terrorist attack."
Dr. Fakhrizadeh, Deputy Minister of Defense and Head of the Research and Innovation Organization of the Ministry of Defense of Iran, who was described by the Supreme Leader Ayatollah Ali Khamenei as "a distinguished nuclear and defense scientist", was assassinated and attained martyrdom on Friday evening, November 27, near the town of Absard, Damavand city, east to Tehran during a terrorist operation by the criminal agents of the Zionist regime.