The United Nations nuclear agency says it urgently wants to find out whether countries besides Libya have acquired designs for nuclear warheads.
ElBaradei is investigating the atomic black market
The head of the International Atomic Energy Agency, Mohammed ElBaradei, said the IAEA was trying to understand the network that gave Libya the technology.
Speaking in the Libyan capital, Mr ElBaradei said some of the same people were involved in supplying Iran.
Libya aims to dismantle its nuclear weapons programme by June, he said.
Mr ElBaradei's visit to Tripoli comes a few days after it emerged that an unpublished IAEA report said Libya had produced a small amount of plutonium but not enough to make a bomb.
June target date
Mr ElBaradei said finding out whether other countries had acquired nuclear weapons technology was "an important and urgent concern for us".
"I think we're coming to the conclusion that it's the same source of supply [in Iran and Libya]," the IAEA head has said.
A disgraced Pakistani scientist, Abdul Qadeer Khan, had admitted selling nuclear secrets to Libya, Iran and North Korea.
Speaking after his talks in Libya, Mr ElBaradei said: "We agreed that we will make every effort to come to a closure on this issue hopefully by June, by our June [IAEA] Board of Governors [meeting]".
He discussed the Libyan programme with Deputy Prime Minister Matoug M Matoug.
Earlier, Mr ElBaradei said Libya might be allowed to continue nuclear research, provided it was for peaceful purposes.
"They [the Libyans] want to keep their research reactor, which is legitimate," he said.
And the IAEA would support Tripoli's wish to "continue with extended peaceful use activities... once we eliminate the military-related programmes".