A planeload of North Korean arms seized in Bangkok was reportedly bound for Iran, which has been buying up large amounts of weaponry in recent months as it braces for a possible onslaught by Israel, and possibly the United States.

Mystery has shrouded the destination of the Georgian-registered Ilyushin Il-76 cargo plane that was found be to carrying 35 tons of arms, including surface-to-air missiles and rocket launchers, in 12 crates when it was detained during a refueling stop on Dec. 11 following a tip-off from U.S. intelligence.

The five-man crew, all former Soviet air force members from Belarus and Kazakhstan, are in police custody and claim they thought they were hauling oil-field equipment.

According to two organizations that monitor international arms transfers -- TransArms in Chicago and the International Peace Information Service in Antwerp, Belgium -- the Ilyushin's flight plan now in the hands of Thai authorities indicates that Iran was the final destination of the deadly cargo, worth an estimated $18 million.

Tehran has been buying unusually large amounts of weapons and military equipment in recent months because of fears the Islamic Republic will be attacked by Israel to knock out its nuclear facilities, and possibly by the United States as well.

North Korea has been identified as a key source of those arms purchases. But in recent months U.S. authorities have also broken up several clandestine Iranian efforts to buy F-4 fighters, helicopters, aircraft components and other military materiel worth $2.5 billion.

The Ilyushin cargo was the first airborne arms shipment from Pyongyang to be seized since U.N. Security Council Resolution 1874 banning arms exports by Pyongyang was passed in June after North Korea conducted missile and nuclear tests.

It authorizes any country to inspect and seize North Korean weapons shipments that pass through its territory, regardless of the cargo's destination.

Cash-starved North Korea is estimated to earn $1 billion a year from arms sales, usually to rogue regimes or insurgent groups, to fund its nuclear program. Its biggest sales are ballistic missiles to Iran and other Middle Eastern states.

The Bangkok seizure was the second shipment of North Korean arms bound for Iran that has been intercepted in recent weeks.

In August authorities in the United Arab Emirates seized a Bahamian-flagged freighter, the ANL Australia, which was found to be carrying military equipment from North Korea to Iran.

Like the Bangkok shipment, that cargo, which included a large quantity of solid-fuel propellant for missiles, was also listed as drilling equipment.

During the summer the U.S. Navy shadowed a North Korean ship suspected of carrying arms to Myanmar. It was refused entry by several ports and eventually turned back.

According to the Stockholm International Peace Research Institute of Sweden, which monitors global arms sales, the Ilyushin seized in Thailand is registered in Georgia to a company called Air West Limited.

It had bought the aircraft from Beibars, a Kazakh company linked to notorious Serbian arms dealer Tomislav Dmanjanovic.

The aircraft had previously been registered with three companies identified by the U.S. Treasury Department's Office of Foreign Assets Control as controlled by Viktor Bout, arguably the world's most infamous arms trafficker.

Although the former Soviet air force officer is not believed to have been involved in the arms shipment seized at Bangkok's Don Muang International Airport, there are some curious links to his gunrunning network and the fleet of aircraft he owns.

Bout was arrested in Bangkok in March 2008 in a sting operation by the U.S. Drug Enforcement Administration on charges of plotting to sell anti-aircraft missiles and other weapons to Colombian rebels listed as terrorists by U.S. authorities.

He was indicted in New York on four charges of terrorism. Last August a Thai court rejected a U.S. extradition request, but Washington is appealing that ruling.

Bout remains behind bars in Bangkok's Klong Prem Central Prison, which is, as fate would have it, where the Ilyushin's crewmen are being held.