UNITED NATIONS (Reuters) - Remnants of four ballistic missiles fired into Saudi Arabia by Yemen s Houthi rebels this year appear to have been designed and manufactured by Riyadh s regional rival Iran, a confidential report by United Nations sanctions monitors said, bolstering a push by the United States to punish the Tehran government. The independent panel of U.N. monitors, in a Nov. 24 report to the Security Council seen by Reuters on Thursday, said it  as yet has no evidence as to the identity of the broker or supplier  of the missiles, which were likely shipped to the Houthis in violation of a targeted U.N. arms embargo imposed in April 2015. Earlier this month, U.S. Ambassador to the United Nations Nikki Haley accused Iran of supplying 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. The report said that monitors had visited two Saudi Arabian military bases to see remnants gathered by authorities from missile attacks on Saudi Arabia on May 19, July 22, July 26 and Nov. 4.  They also visited four  impact points  from the Nov. 4 attack where other remnants of the missiles were identified.  Design characteristics and dimensions of the components inspected by the panel are consistent with those reported for the Iranian designed and manufactured Qiam-1 missile,  the monitors wrote. The Qiam-1 has a range of almost 500 miles and can carry a 1,400-pound warhead, according to GlobalSecurity.org public policy organization. Saudi-led forces, which back the Yemeni government, have fought the Iran-allied Houthis in Yemen s more than two-year-long civil war. Saudi Arabia s crown prince has described Iran s supply of rockets to the Houthis as  direct military aggression  that could be an act of war. Iran has denied supplying the Houthis with weapons, saying the U.S. and Saudi allegations are  baseless and unfounded.  Iran s mission to the United Nations did not immediately respond to a request for comment on the U.N. monitors report.  Another ballistic missile was shot down on Thursday near the southwestern Saudi city of Khamis Mushait, the Saudi-owned al-Arabiya channel reported. The U.N. monitors said they gathered evidence that the missiles were transferred to Yemen in pieces and assembled there by missile engineers with the Houthis and allied forces loyal to Yemen s former President Ali Abdullah Saleh.  The panel has not yet seen any evidence of external missile specialists working in Yemen in support of the Houthi-Saleh engineers,  the monitors wrote.     They visited Saudi Arabia after the monitors called on the coalition to provide evidence backing Riyadh s claim that Iran was supplying missiles to the Houthis, warning that a failure to do so would violate a U.N. resolution. They said the missiles most likely were smuggled into Yemen along  the land routes from Oman or Ghaydah and Nishtun in al Mahrah governorate (in Yemen) after ship-to-shore transshipment to small dhows, a route that has already seen limited seizures of anti-tank guided weapons.  The monitors also said that while  concealment in cargo of vessels offloading in the Red Sea ports is unlikely, it cannot be excluded as an option.  The Saudi-led coalition used the Nov. 4 missile attack to justify a blockade of Yemen for several weeks, saying it was needed to stem the flow of arms to the Houthis from Iran. The United Nations had said the blockade could spark the largest famine the world has seen in decades. Some 7 million people in Yemen are on the brink of famine, and nearly 900,000 have been infected with cholera. 