The United States on Monday led western calls for tougher UN action on Iran's arms supplies to Syria and its Lebanese ally Hezbollah.
The calls came as Russia blocked a UN panel's unanimous ruling that a ballistic missile launch by Iran was a breach of international sanctions, diplomats said.
The US government called on the UN Security Council and its sanctions committee to tackle Iran's alleged breach of UN measures with "increased vigor."
"The committee should also address the steady of flow of Iranian arms, military support, advisors and training to groups in Syria, Lebanon, Gaza, Yemen, Iraq and beyond," said US acting ambassador Rosemary DiCarlo.
Iran has long supplied weapons to President Bashar al-Assad's government "knowing they would be used to massacre the Syrian people," DiCarlo told a Security Council meeting.
The seizure of Iranian arms off the Yemen coast in January "was more than just a sanctions violation, it was an aggressive act to undermine Yemen's transition," said the US envoy.
The vessel was intercepted by the Yemeni coastguard in the Arabian Sea on January 23.
"This council must tackle with renewed urgency, Iranian military assistance to Hezbollah and other armed terrorist groups and should also consider the impact of Iran's actions on the sovereign rights of other countries especially Lebanon," she said.
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Britain's UN ambassador Mark Lyall Grant said there was "credible information that Iran is providing substantial military and financial support to Hezbollah and the syrian regime in contravention of the UN embargo on arms exports by Iran."
French political counsellor, Philippe Bertoux, also said that the council must "assume its responsibilities" over Iran's sanctions breaches.
Iran already faces widespread sanctions over its nuclear program and a UN panel of experts ruled in January that the firing of a Shahab ballistic missile by Iran in July last year was a breach of UN sanctions, diplomats said.
However, Russia, supported by China, blocked the usual consensus publication of the experts report, even though a Russian and a Chinese expert are on the panel, diplomats said.
Gary Quinlan, the Australian ambassador to the UN who chairs the Security Council's Iran sanctions committee, said only that "some members" do not back the experts view.
Britain's Lyall Grant said the Security Council should add individuals linked to the launches to UN sanctions lists. DiCarlo of the United States said the missile launch was a "clear violation" of UN resolution 1929.
Petr Ilyichev, a deputy UN ambassador for Russia, spoke only of a "possible violation." He did not confirm his country had held up the experts' report but said the sanctions committee decisions must be based on "reliable and verified information."
China's deputy UN ambassador Wang Min gave a similar message. China, he said, was "not in favor of increased pressure or new sanctions against Iran."
No Iranian representatives were at the meeting.