Libyan Foreign Minister Abdel Rahman Shalgham has said the country will sign a protocol allowing short-notice inspections of its nuclear sites.
ElBaradei says Libya has admitted having undeclared materials
"Libya will co-operate with the [UN's nuclear] agency with complete transparency," he told reporters.
He also called on Israel to dismantle its weapons of mass destruction.
The head of the UN nuclear watchdog, Mohammed ElBaradei, who arrived in Libya earlier in the day, praised Tripoli for its openness.
"Libya is opening its door for us and we will take full of advantage to implement our mandate," he said.
Mr ElBaradei is leading a team from the International Atomic Energy Agency (IAEA) to assess the state of Libya's nuclear facilities.
The visit comes days after Tripoli's decision to scrap plans for weapons of mass destruction.
The IAEA head has said weapons experts could begin their work immediately after his visit.
In an interview with Reuters news agency before leaving Vienna, Mr ElBaradei said he did not think Libya had enriched any uranium - a step that could have been seen as a first move towards building an atomic bomb.
"From the look of it, they were not close to a weapon, but
we need to go and see it and discuss the details with them," he said.
IAEA spokesman Mark Gwozdecky said the purpose of the visit "will be to initiate an in-depth process of verification of all of Libya's past and present nuclear activities... and pave the road for the upcoming inspections."
"We have no programme yet. We shall get it when we get there," he added.
Mr ElBaradei said on Monday he would discuss with the IAEA board to what extent Libya had fallen short of commitments to the nuclear Non-Proliferation Treaty.
"The Libyans told us that there had been some material that should have been declared and was not declared," he said.
"Clearly there were some cases of failures to report. We will report to the board at our next meeting in March."
Last week, Libya offered to scrap its weapons of mass destruction programme and sign up to the IAEA's inspections protocol.
Libya is already a signatory of the Nuclear Non-Proliferation Treaty (NPT).
But the protocol allows for tougher, short-notice visits of nuclear sites by IAEA experts.
The dismantling of Libya's nuclear programme is likely to be a long, drawn-out process:
- Mr ElBaradei goes to Libya for general talks and requests an overall account of Libya's nuclear programme
- Libya will account for its entire nuclear programme
- The IAEA will conduct a series of inspections, to verify that what the Libyans declare is accurate
- The dismantling process will be carried out, probably by Libyans
- There will be continuous monitoring by the IAEA to ensure that no new nuclear programmes are set up.
Libya's pledge to abandon its weapons of mass destruction programmes followed nine months of secret negotiations with Britain and the US.