UNITED NATIONS (Reuters) - The United States accused Iran on Tuesday of supplying Yemen s Houthi rebels with a missile that was fired into Saudi Arabia in July and called for the United Nations to hold Tehran accountable for violating two U.N. Security Council resolutions.  U.S. Ambassador to the United Nations Nikki Haley said information released by Saudi Arabia showed the missile fired in July was an Iranian Qiam, which she described as  a type of weapon that had not been present in Yemen before the conflict.  Saudi-led forces, which back the government in neighboring Yemen, have been targeting the Iran-allied Houthis in a more than two-year war. Saudi Arabia s crown prince on Tuesday described Iran s supply of rockets to the Houthis as  direct military aggression  that could be an act of war. Haley said that by providing weapons to the Houthis, Iran s Islamic Revolutionary Guard Corp s had violated two U.N. resolutions on Yemen and Iran. She said a missile shot down over Saudi Arabia on Saturday  may also be of Iranian origin.       We encourage the United Nations and international partners to take necessary action to hold the Iranian regime accountable for these violations,  Haley said. It was not immediately clear what action the United States was calling for.  Saudi U.N. Ambassador Abdallah Al-Mouallimi echoed Haley s call for U.N. action against Iran in a letter to the U.N. Security Council and Secretary-General Antonio Guterres later on Tuesday, seen by Reuters.  He said the missile fired on Saturday  may amount to a war crime  and that Saudi Arabia was  taking appropriate measures to respond to these terrorist acts.  Iran s U.N. Ambassador Gholamali Khoshroo also wrote to the Security Council and Guterres on Tuesday, rejecting the accusations by Saudi Arabia as  baseless and unfounded.   Iran calls for self-restraint and wisdom instead of provocation and threat that may bring further instability to this already volatile region,  Khoshroo wrote in the letter, seen by Reuters.  Under a U.N. resolution that enshrines the Iran nuclear deal with world powers, Tehran is prohibited from supplying, selling or transferring weapons outside the country unless approved in advance by the U.N. Security Council. A separate U.N. resolution on Yemen bans the supply of weapons to Houthi leader Abdul-Malik al-Houthi, two Houthi commanders, Yemen s former President Ali Abdullah Saleh, his son, and  those acting on their behalf or at their direction.  The United States could propose people or entities to be blacklisted by the Security Council s Yemen sanctions committee, a move that would need consensus approval by the 15-members.  Or it could put forward a new Security Council resolution to impose sanctions on Iran. To pass, a resolution needs nine votes in favor and no vetoes by the United States, Britain, France, China or Russia. 