Russian Ambassador Vassily Nebenzia said it was unclear whether missiles and weaponry used by the rebels were sent by Iran or whether they were shipped before the arms embargo on Yemen was imposed in 2015, casting doubt over the findings of a UN panel of experts.

"Iran is vehemently denying it is supplying anything to Yemen," Nebenzia told two reporters.

"Yemen hosts a pile of weapons from the old days. Many countries were competing to supply weapons to Yemen during the time of president Saleh, so I cannot give you anything conclusive."

Ali Abdullah Saleh, who ruled Yemen from 1990 to 2012, was killed in December by his erstwhile Huthi rebel allies.

Asked whether the case had been made for action against Iran, the ambassador answered "no."

Nebenzia joined UN Security Council ambassadors on a visit to Washington this week to inspect debris from missiles that the United States says were supplied by Iran to the Huthis.

The ambassadors had lunch with President Donald Trump, who urged the council to take steps to counter "Iran's destabilizing activities" in the Middle East.

- Lack of evidence -

A recent report by the UN panel of experts bolstered the US claims when it concluded that Iran had violated the arms embargo on Yemen by failing to block missile supplies to the rebels.

The Trump administration has said it will seek action at the Security Council against Iran, although it has yet to specify what those measures may be.

"If there is something we will see. How can we pass judgment prematurely before we know what it is about," Nebenzia said.

Russia has the power to block sanctions by resorting to its veto power as one of the five permanent Security Council members along with Britain, China, France and the United States.

Last month, US Ambassador Nikki Haley presented the missile fragments as "undeniable" evidence that Iran had fabricated a ballistic missile fired by Yemen's Huthi rebels at Saudi Arabia in November.

Kazakh Ambassador Kairat Umarov, this month's council president who also traveled to Washington to inspect the missile debris, said there was no strong evidence of a supply route from Iran to the Huthis.

"It would be good of course to have very conclusive evidence to say how this kind of armaments appeared in Yemen, because at this point in time, there is no information about that," Umarov told reporters.

"We understand that this was produced in Iran, but (there is) no information on how it was sent to Yemen."