Lord Mandelson clarified his dealings in a letter to a national newspaper
Lord Mandelson has admitted meeting Russian billionaire Oleg Deripaska two years earlier than previously revealed.
Controversy has surrounded events at a summer party on board the tycoon's yacht attended by Lord Mandelson, then European Trade Commissioner.
EU officials previously said the two had met socially in 2006 and 2007.
But in a letter to the Times, Lord Mandelson said they first met in 2004 and accepts people may have been misled by a statement issued by his officials.
The length and nature of their relationship is central to questions over whether Lord Mandelson, while European Trade Commissioner, faced conflicts of interest when dealing with matters connected to Mr Deripaska.
Earlier this month, the European Commission cleared Lord Mandelson of any inappropriate links with the tycoon, whose business benefited from a December 2005 decision to ease import duties on Russian aluminium.
Lord Mandelson - now UK business secretary - had rejected accusations that he had intervened to get tariffs reduced on behalf of Mr Deripaska, who has an estimated £16bn fortune and owns the world's biggest aluminium producer UC Rusal.
But a newspaper report in the Guardian suggested officials who cleared the peer had not been aware of a previous meeting between the two men, before he took up his post as trade commissioner.
BBC political correspondent Vicky Young said the reduction of tariffs saved Mr Deripaska millions of pounds.
"The fact that he met him earlier than previously thought means it coincides with the time when these tariffs were discussed," she added.
However Director General for Trade in the European Commission, David O'Sullivan, reiterated on Saturday that there was "no political interference by Peter Mandelson" in the tariff decisions.
He said they were "subject to numerous discussions in Council and final decisions were reached in an entirely standard and routine manner".
Liberal Democrat MP Norman Baker has now called for Lord Mandelson to provide further details of the meetings.
Asked for comment on Mr Mandelson's meetings, Prime Minister Gordon Brown said: "This was already investigated by the European Commission when he was a commissioner and the answer was nothing untoward happened. That's where the story lies."
In the letter, Lord Mandelson, who made a surprise return to the Cabinet earlier this month, said journalists had been asking about his meetings with Mr Deripaska.
He wrote: "During the weekend when I moved from Brussels to London and prior to me being admitted to hospital for an urgent medical procedure, a statement was released to the press which said I had had meetings with Mr Deripaska in 2006 and 2007.
"Some people formed the reasonable view, therefore, that my first meeting with him was in 2006. This is not the case: To the best of my recollection we first met in 2004 and I met him several times subsequently."
The row centres on a party on board Mr Deripaska's yacht
Lord Mandelson, now business secretary, also wrote how he had met a great number of business people around the world while he was EU commissioner.
"I think this adds to what I bring to my job now," he added.
He went on to say he would "ensure no conflict of interest, or perception of such" arises from any past or future contacts and would take advice from his permanent secretary "at all times".
He added: "As business secretary I will continue to act with the public interest in mind, as the public has every right to expect."
But Mr Baker said: "The earlier statement about Mr Mandelson's meetings Mr Deripaska was clearly spin, which is now becoming un-spun.
"Peter Mandelson does not say whether these meetings were in an office in Brussels with other EU officials, or on his yacht eating canapes.
"He must urgently publish a full list of each meeting detailing where these meeting were and what was discussed."
The row about the party on board Mr Deripaska's yacht relates to allegations that the shadow chancellor George Osborne, who was also attending, attempted to solicit a £50,000 Tory donation from him. Mr Osborne has firmly denied the claims.