The aircraft, an Ilyushin 62 owned by Air Koryo, the North Korean state airline, made a stopover in Myanmar on August 7 and sought air traffic controllers' permission to fly over India en route to Iran, the newspaper has reported.

Initially the air traffic control in Kolkata gave the plane the go-ahead, but around noon on August 7, the Directorate General of Civil Aviation in New Delhi messaged Kolkata cancelling the permission, reports WSJ.

The newspaper in fact had a supervisor at the Kolkata air traffic control, one Mr Guin, review the flight records of Air Koryo's Flight 621 for August 7 and confirm the incident. Guin told WSJ that the denial of permission was passed on to air traffic control officials in Yangon, who sent back the flight.

While neither the US administration nor the Prime Minister's Office responded to the report, or described the cargo on the plane, officials in the know told the WSJ that the action was part of the Bush administration's Proliferation Security Initiative.

Action under this initiative points to one of the three possibilities: the cargo contained nuclear material, long-range missiles, or other lethal cargo, the officials said. A 2006 UN Security Council resolution prevents North Korea from sale and purchase of long-range missiles. In 2007 also, the US prevented a Syrian plane from landing in Pyongyang, convinced that it was part of the missile trade.

The US had for long held Pyongyang guilty of supplying missile technology to nations like Iran, Syria and Libya. But in October, convinced that engaging North Korea was essential to containing its nuclear programme, the US reached a deal with Kim Jong Il's government that eventually shuts down its N-programme.

But what the deal doesn't focus on is Pyongyang's robust missile programme.