Tony Blair visited Libya for talks with Col Muammar Gaddafi in 2008 and 2009, his spokesman has confirmed.
Papers found in Tripoli show the ex-PM used the ousted leader's private jet to attend, the Sunday Telegraph reports.
Mr Blair apparently did not mention the visits on websites publicising his activities as Middle East peace envoy.
Talks focused on African politics. The Lockerbie bomber's status was raised but Mr Blair stressed it was a case for Scotland's leaders, his spokesman said.
At the time, Libya was threatening to sever commercial links with Britain if Abdelbaset al-Megrahi was not released from the Scottish prison where he was held for killing 270 people in the 1988 bombing of a Pan Am flight.
He was eventually freed from his life sentence on health grounds in August 2009 - four months after Mr Blair visited Libya - after the Scottish Executive was advised Megrahi had just three months to live.
Megrahi remains alive but is said to be seriously ill with prostate cancer.
'Delighted and grateful'
The Sunday Telegraph said the documents showed Mr Blair negotiated to fly to Tripoli from Sierra Leone in west Africa in a jet provided by Col Gaddafi.
It said one June 2008 letter, sent on notepaper headed Office of the Quartet Representative - Mr Blair's title as peace envoy - was sent to the Libyan ambassador to the UK.
"Mr Blair is delighted that The Leader is likely to be able to see him during the afternoon of 10 June and he is most grateful that the Libyan authorities have kindly offered an aircraft to take him from Freetown to Tripoli and back to London," it stated.
Details of the 2009 meeting are contained in an exchange of emails between Mr Blair's events organiser and the former British ambassador to Libya, in which accommodation and transport are discussed, the newspaper said.
A spokesman for Mr Blair said he had talked to Col Gaddafi about African politics - Libya having been head of the African Union, the Middle East and reform in Libya.
"Of course the Libyans, as they always did, raised Megrahi. Mr Blair explained, as he always did, in office and out of it, that it was not a decision for the UK government but for the Scottish Executive."
The spokesman said no business deals were discussed and that Mr Blair had never had any role with the Libyan government or Libyan Investment Authority, nor any commercial relationship with a Libyan company.
As world governments were engaging with Libya and Col Gaddafi was being received in European capitals, "there was... no reason whatsoever for not continuing to engage with him", he added.