While Iran denies arming the Al Houthis in Yemen, the United States and Saudi Arabia claim that the evidence of an arms connection is irrefutable.

On Monday, the Saudi-led coalition accused Iran of being behind a barrage of Yemeni missile attacks on the kingdom, and threatened retaliation.

On Wednesday, the UN Security Council expressed grave concern at reports of violations of an U.N. arms embargo on Houthi leaders. The council condemned “in the strongest possible terms” the missile attacks launched by the Al Houthis on Saudi Arabia, saying they posed a threat to regional security.

On Sunday, Saudi forces intercepted seven missiles fired by the Al Houthi rebels toward cities in Saudi Arabia, including the capital Riyadh, killing one person. Saudi forces said they shot down three missiles over Riyadh shortly before midnight, and debris fell on a home in the capital, killing an Egyptian man and wounding two others. Air defenses also repelled missiles fired at the southern Saudi cities of Najran, Jizan and Khamis Mushait.

The 15-member Security Council issued a statement expressing alarm at a Houthi threat to continue such attacks in the region. The United Nations considers this war to be the world’s most urgent humanitarian crisis, as millions of Yemenis live under threat of mass starvation and disease, while combatants cut off food and medical supplies.

“The members of the Security Council expressed their grave concern at the continued deterioration of the humanitarian situation in Yemen and the devastating humanitarian impact of the conflict on civilians,” the statement said. However, the U.N. Security Council statement on Wednesday did not name who is violating the arms embargo.

The Houthis say their movement is a national revolution against corruption, and deny Iranian influence, but the three-year conflict pits a coalition of Sunni Arab states who are friendly to the West, against the Houthis, a movement sympathetic to Iran.

In reports to the Security Council in January, independent U.N. experts stated that Iran had violated U.N. sanctions on Yemen because “it failed to take the necessary measures to prevent the direct or indirect supply, sale or transfer” of ballistic missiles and other equipment to the Houthi group.

US President Trump’s administration has been lobbying for Iran to be held accountable at the United Nations. In fact, Trump has threatened to abandon the 2015 nuclear deal between Iran and world powers if “disastrous flaws” are not fixed.

A western bid for the United Nations Security Council to call out Tehran for failing to prevent its weapons from falling into the hands of the Houthis was vetoed by Russia last month.