Saudi Arabia is accusing Iran of supplying weapons to Shiite Houthi rebels in Yemen and is urging the U.N. Security Council to impose sanctions on Iran for violating an arms embargo.

Sunni-majority Saudi Arabia and Shiite-majority Iran are regional rivals and back opposing sides in Yemen and Syria.

Saudi Ambassador Abdallah Al-Mouallimi said in a letter to the council that smuggling arms to Houthi rebels violates council resolutions and constitutes "a direct and tangible threat" to Saudi Arabia, Yemen, the region and international peace and security.

He said in the letter obtained late Saturday by The Associated Press that the Houthis and their supporters "must be held accountable for their continued irresponsible and criminal behavior."

Iran's U.N. Mission "categorically" rejected the allegations, saying the claims have not been independently verified.