UNITED NATIONS (Reuters) - U.N. Secretary-General Antonio Guterres warned on Wednesday that any issues not directly related to the Iran nuclear deal “should be addressed without prejudice to preserving the agreement,” his spokesman said amid U.S. concerns with Tehran.

U.N. Secretary General Antonio Guterres speaks as he visits the reinsertion centres of former FARC rebels in Buenavista, Colombia January 14, 2018. REUTERS/Jaime Saldarriaga

U.S. President Donald Trump said on Friday that European allies and Congress have to work with him to fix “the disastrous flaws” in the nuclear pact or face a U.S. exit. Trump wants it strengthened with a separate agreement within 120 days.

Trump also views Iran as a rising threat in the Middle East and the United States has accused Tehran of violating U.N. resolutions by supplying weapons to Houthi rebels in Yemen. Iran has denied supplying the Houthis.

Most U.N. and Western sanctions on Iran were lifted under the nuclear deal. However, Iran is still subject to a U.N. arms embargo and other restrictions, which are not technically part of the nuclear deal.

“The (nuclear deal) constitutes a major achievement of nuclear non-proliferation and diplomacy, and has contributed to regional and international peace and security,” U.N. spokesman Stephane Dujarric told reporters on the second anniversary of the implementation of the deal between Iran and key world powers.

Guterres called for concerns relating to the implementation of the nuclear deal “to be addressed through the mechanisms established by the agreement,” Dujarric said.

The parties to the nuclear deal created a joint commission to handle any complaints of breaches. If the complaining state is not satisfied with how the commission addresses its concerns, it can then take its grievance to the U.N. Security Council.

If the Security Council receives a complaint of a breach it would then need to vote within 30 days on a resolution to extend sanctions relief. If it fails to vote, the sanctions would be automatically re-imposed.

Iran says its nuclear program is only for peaceful purposes and that it will stick to the accord as long as the other signatories respect it, but will “shred” the deal if Washington pulls out.

The U.S. administrations of both Trump and his predecessor Barack Obama, together with European allies, have also raised concerns over ballistic missile tests carried out by Iran.

Under a U.N. resolution enshrining the nuclear deal, Iran is also “called upon” to refrain from work on ballistic missiles designed to deliver nuclear weapons for up to eight years. Some states argue that language does not make it obligatory.

Iran has denied that it has missiles designed to carry nuclear warheads.

Senior U.S. administration officials said last week that Trump will work with European partners on a follow-on agreement that enshrines certain triggers that Iran cannot exceed related to ballistic missiles.