UN nuclear experts have started visiting sites related to Libya's weapons of mass destruction programme.
Mohamed ElBaradei may meet Colonel Gaddafi
They are also talking to officials involved in the now-defunct plans.
Earlier this month Libya announced it would abandon its nuclear, chemical and biological weapons aspirations and invited international checks.
The inspectors visited four nuclear sites near Tripoli on Sunday, but there is no word on what they were shown, the BBC's Peter Biles reports.
The team led by Mohamed ElBaradei, head of the United Nations' International Atomic Energy Agency (IAEA), arrived in Libya on Saturday.
Mr ElBaradei is due to return to Vienna on Monday, but some of his colleagues will remain in Libya, to develop a work plan for further IAEA inspections and monitoring.
Mr ElBaradei held talks with Foreign Minister Abdel Rahman Shalgham and Deputy Prime Minister Matouk Mohamed Matouk, who was in charge of the nuclear programme.
Libya has promised full co-operation and transparency.
It is thought to have developed a uranium enrichment programme, but is reported to have got only as far as the laboratory phase.
Libya now hopes to set an example to other countries in stopping the proliferation of nuclear weapons, our correspondent reports from Tripoli.
There is speculation that Mr ElBaradei will also meet Libyan leader Muammar Gaddafi, who is believed to be trying to return his country to the international community after years of isolation.
Promise of 'transparency'
Mr ElBaradei said he did not believe Libya was close to making a nuclear bomb, but there needed to be a stringent verification process.
"Minister Shalgham has assured me... that Libya will co-operate with us with full transparency, will lend its full co-operation to our activities, and I am very pleased to hear that," he said after his first meeting.
Mr Shalgham pledged that Libya would agree to allow inspections of its nuclear sites at short notice, going further than its commitments as a signatory to the Nuclear Non-Proliferation Treaty (NPT).
He also called on Israel to dismantle its weapons of mass destruction - a programme which is widely suspected but not acknowledged.
Mr ElBaradei said he would prepare a report to be submitted to the IAEA board of governors in March.
His trip came just days after the surprise announcement that Libya would give up its quest to develop nuclear, chemical and biological weapons after nine months of secret talks with Britain and the United States.