UNITED NATIONS - A shipment of weapons from North Korea seized by Thai authorities last month were headed for Iran, according to a confidential report the Thai government sent to a U.N. Security Council committee.

Thai authorities seized more than 35 tons of arms from a cargo plane they said had come from North Korea, and arrested its five crew members after the aircraft made an emergency landing at a Bangkok airport in December.

The report to the Security Council's North Korea sanctions committee, seen by Reuters on Saturday, said the shipment included rockets, fuses, rocket launchers and rocket-propelled grenades.

The cargo plane departed from Pyongyang and was en route to Mehrabad airport in Tehran, the report said. The shipping firm was listed as Korea Mechanical Industry Co.

The movement of North Korean arms to Iran appears to have been an effort to violate U.N. sanctions against North Korea that was foiled by the Thai government, diplomats said. Although Iran is subject to separate U.N. sanctions because of its nuclear program, it is not forbidden to import arms.

Council diplomats said on condition of anonymity that the sanctions committee was expected to discuss the Thai report next month when it considers its latest quarterly report, due on February 11.

The committee will probably send letters to Pyongyang and Tehran for details on the shipment, the Western diplomats added.

North Korea was hit with fresh U.N. sanctions last year to punish it for a nuclear test in May 2009, its second atomic detonation. The expanded measures are aimed at cutting off its arms sales, a vital export estimated to earn the destitute state more than $1 billion a year.

North Korea's biggest arm sales come from ballistic missiles, with Iran and other Middle Eastern states as customers, according to U.S. government officials.

The U.N. sanctions and the cut-off of handouts from South Korea have dealt a heavy blow to the North, which has an estimated GDP of $17 billion, and may force it back into nuclear disarmament talks in the hopes of winning aid, analysts said.

(Reporting by Louis Charbonneau; Editing by Xavier Briand)