UNITED NATIONS (Reuters) - Iran violated a U.N. Security Council resolution in October by test firing a missile capable of delivering a nuclear warhead, a team of sanctions monitors said, leading to calls in the U.S. Congress on Tuesday for more sanctions on Tehran.

An Iranian Emad rocket is launched as it is tested at an undisclosed location October 11, 2015. REUTERS/farsnews.com/Handout via Reuters

The White House warned that it would not rule out additional steps against Iran over the test of the medium-range Emad rocket.

The Security Council’s Panel of Experts on Iran said in a confidential new report, first reported by Reuters, that the launch showed the rocket met its requirements for considering that a missile could deliver a nuclear weapon.

“On the basis of its analysis and findings the Panel concludes that Emad launch is a violation by Iran of paragraph 9 of Security Council resolution 1929,” the panel said.

Diplomats say the rocket test on Oct. 10 was not technically a violation of the July nuclear deal between Iran and six world powers but the U.N. report could put President Barack Obama’s administration in an awkward position.

Iran has said that any new sanctions would jeopardize the nuclear deal but if Washington failed to call for sanctions over the Emad launch it would likely be perceived as weakness.

Diplomats say it is possible for the U.N. sanctions committee to blacklist additional Iranian individuals or entities, something Washington and European countries are likely to ask for. However, they said Russia and China, which dislike the sanctions on Iran’s missile program, might block any such moves.

The panel’s 10-page report was dated Dec. 11 and went to members of the United Nations Security Council’s Iran sanctions committee in recent days. The report came up on Tuesday when the 15-nation council discussed the Iran sanctions regime.

It said the panel considers ballistic missiles capable of delivering nuclear weapons to be those that can deliver at least a 500 kg (1,102 lb) payload within a range of at least 300 km (186 miles).

“The Panel assesses that the launch of the Emad has a range of not less than 1,000 km with a payload of at least 1,000 kg and that Emad was also a launch ‘using ballistic missile technology’,” the report said.

The panel noted that Iranian rocket launches from 2012 and 2013 also violated the U.N. ban on ballistic missile tests.

CONGRESS RESPONSE

Republicans in Congress who disapprove of the Iran nuclear deal were seizing on the U.N. panel’s findings as grounds for additional congressional U.S. sanctions. Even some Democrats supported unilateral U.S. action on the missile violations.

Democratic U.S. Senator Chris Coons, a member of the foreign relations panel who backed the Iran nuclear deal, said it was up to the Security Council to act but if it did not, the United States should, including by imposing direct sanctions on Iranians who are responsible for the missile tests.

While ballistic missile tests may violate U.N. Security Council sanctions, council diplomats note that such launches are not a violation of the nuclear deal, which is focused on specific nuclear activities by Iran.

Iran, which has always rejected sanctions against as illegal and unjustified, has repeatedly made clear it has no intention of complying with the restrictions on its missile program.

Asked about the panel’s report, British U.N. Ambassador Matthew Rycroft told reporters it was “absolutely crucial that the Security Council upholds its responsibilities and does respond effectively to what appears to have been a breach.”

The expert panel did not mention a second reported missile test that Iran carried out last month. The panel produced its report after the United States, Britain, France and Germany in October called on the U.N. sanctions committee to take action in response to Iran’s test of an Emad missile.

Iran’s U.N. mission did not respond to a request for comment. In October, Tehran disputed the Western assessment that the missile was capable of delivering a nuclear warhead.

Security Council resolution 1929, which bans ballistic missile tests, was adopted in 2010 and remains valid until the nuclear deal is implemented.

Under that deal, most sanctions on Iran will be lifted in exchange for curbs on its nuclear program. According to a July 20 resolution endorsing the deal, Iran is still “called upon” to refrain from work on ballistic missiles designed to deliver nuclear weapons for up to eight years.

Although the section of the July 20 resolution applying to missiles is weaker and more limited than the total ban in resolution 1929, U.S. officials say they will continue to act as if there was a de facto total ban on ballistic missile tests by Iran in the years to come once the nuclear deal is implemented.

The experts’ report also noted that ballistic missile launches would still be covered by the July 20 resolution.

U.S., Iranian and Russian officials have said they expect the full implementation of the Iran deal, including the lifting of sanctions, to happen early next year once the U.N. nuclear watchdog confirms Iranian compliance with the agreed restrictions on its atomic work.

Earlier on Tuesday, the U.N. nuclear watchdog’s 35-nation board in Vienna closed its investigation into whether Iran sought atomic weapons, opting to back the international deal with Tehran rather than dwell on Iran’s past activities, diplomats said.

U.S. Secretary of State John Kerry welcomed the decision to close the investigation into whether Iran once had a secret nuclear weapons program.