By Michelle Nichols

UNITED NATIONS (Reuters) -U.S. strikes on Iran's nuclear facilities "effectively fulfilled our narrow objective: to degrade Iran's capacity to produce a nuclear weapon," acting U.S. envoy to the U.N. Dorothy Shea told the United Nations Security Council on Tuesday.

"These strikes – in accordance with the inherent right to collective self-defense, consistent with the U.N. Charter – aimed to mitigate the threat posed by Iran to Israel, the region and to, more broadly, international peace and security," Shea told the 15-member council.

U.S. President Donald Trump has said the strikes over the weekend "completely and totally obliterated" Iran's key nuclear enrichment facilities. Earlier on Tuesday he announced that a ceasefire between Iran and Israel had started.

"I think it's still early to assess all the strikes. We know we were able to push back the (nuclear) program. We were able to remove the imminent threat that we had," Israel's U.N. Ambassador Danny Danon told reporters on Tuesday.

A preliminary U.S. intelligence assessment has determined that U.S. strikes over the weekend on Iranian nuclear facilities have set back Tehran's program by only a matter of months, three sources with knowledge of the matter told Reuters.

"Iran emerged proud and steadfast in the face of this criminal aggression. This proves one simple truth more clearly than ever: Diplomacy and dialogue are the only path to resolving the unnecessary crisis over Iran's peaceful program," Iran's U.N. Ambassador Amir Saeid Iravani told the Security Council.

'REGRETTABLE'

The U.N. Security Council met on Tuesday to discuss implementation of a resolution adopted in 2015 to enshrine Iran's nuclear deal with world powers, which lifted sanctions on Tehran in exchange for restrictions on its nuclear program.

Trump quit the deal in 2018, during his first term, and restored all U.S. sanctions on Tehran. Iran then began moving away from its nuclear-related commitments under the accord.

U.N. political affairs chief Rosemary DiCarlo told the Security Council on Tuesday that the objectives of the Iran nuclear deal and the U.N. resolution "have yet to be fully realized," adding: "This is regrettable."

Since April, Iran and the U.S. have held indirect talks aimed at finding a new diplomatic solution regarding Iran's nuclear program. Tehran says its program is peaceful. The U.S. wants to ensure it cannot build a nuclear weapon.

However, talks were suspended after Israel began targeting Iran's nuclear and ballistic missile programs on June 13. Danon told the Security Council on Tuesday that Iran was working on the key elements for a nuclear bomb.

Citing reports by the International Atomic Energy Agency, Russia's U.N. Ambassador Vassily Nebenzia said Western nations were asserting "falsehoods" to "an audience that has not read these reports or that did not understand this issue."

The IAEA has said it cannot guarantee Iran's nuclear activity is entirely for peaceful purposes but it also has no credible indications of a coordinated nuclear weapons program.

(Reporting by Michelle Nichols; Editing by Kanishka Singh, Daniel Wallis and Cynthia Osterman)