The UN atomic agency is investigating reports that North Korea secretly sent uranium to Libya when Tripoli was trying to develop nuclear weapons.
Libya has opened up its research facilities to international inspection
Diplomats quoted by The New York Times said the agency had found evidence that Pyongyang provided Libya with nearly two tons of uranium in early 2001.
Libya handed over the uranium to the US in January this year, after deciding to abandon its quest for nuclear weapons.
Pakistan's former nuclear chief AQ Khan ran a huge secret nuclear black market.
The UN's International Atomic Energy Agency (IAEA) is investigating various leads emerging from interviews with former members of Mr Khan's network and their associates.
IAEA spokesman Mark Gwozdecky told BBC News Online that the investigation "spans three continents and involves entities or individuals in at least eight countries".
He said the IAEA had not yet reached any conclusions about the alleged North Korea connection.
The newspaper said the uranium shipped to Libya could not be used as nuclear fuel unless it was enriched in centrifuges, which the Libyans were assembling as part of a $100m programme to purchase equipment from the Khan network.
It quoted US officials as saying the discovery of a North Korean connection was an intelligence success springing directly from Libya's decision to dismantle its nuclear weapons programme and the subsequent drive to smash the Khan network.
Abdul Qadeer Khan has admitted selling nuclear secrets to Libya, Iran and North Korea.
Intelligence services are trying to find out whether North Korea made similar clandestine sales to other countries or even terror groups.
According to the IAEA, Libya produced a small amount of plutonium - but not enough to make a bomb.