By Stephanie Kirchgaessner in Washington

Mark Penn, chief executive of Burson-Marsteller, a global public affairs and lobbying company owned by Britain’s WPP and Mrs Clinton’s top aide, apologised for the meeting with the Colombian representative.

“The meeting was an error in judgment that will not be repeated and I am sorry for it. The Senator’s well known opposition to this trade deal is clear and was not discussed,” he said in a statement.

Burson-Marsteller was hired by the Colombian government as part of a multi-million dollar contract to help it secure approval in Congress of a trade agreement that has been criticised by both Mrs Clinton and her Democratic rival, Barack Obama. Mr Penn’s meeting with the official occurred just days before President George W. Bush is expected to send the agreement to Congress.

A colleague of Mr Penn said the executive, who is not listed as working on the account in Burson-Marsteller’s public filings, was not actively working on the Colombia account and had attended a breakfast meeting with the ambassador as a “courtesy” to a colleague.

The Clinton campaign said Mrs Clinton would vote against the deal and that she and Mr Penn had not discussed the trade agreement.

The incident comes at a difficult time for Mrs Clinton, who has been accused by Mr Obama’s campaign of misrepresenting her record on the North American Free Trade Agreement, which she has said she opposed when it was agreed under the administration of her husband, Bill Clinton.

Mr Obama has also been forced to deny accusations that promises he has made to renegotiate Nafta were empty political rhetoric.

Change to Win, a seven-member labour alliance, said the revelation about Mr Penn’s meeting - which was first reported in the Wall Street Journal - was “outrageous” and that Mr Penn ought to be sacked.

“How can we trust that a President Hillary Clinton would stand strong against this trade deal when her top advisor is being paid by Colombia to promote it?” said Jim Hoffa, the general president of the Teamsters.

The incident was not the first time that critics have assailed Mr Penn for his duel role as chief executive of a powerful Washington lobbying firm and Mrs Clinton’s top strategist.

At the heart of the criticism are allegations that Mrs Clinton espouses one set of values, while Mr Penn’s company works on behalf of clients that undermine those values, such as Cintas, a food services company that has fought unionisation efforts by its workers.

In an interview with the Financial Times last year, Mr Penn said he personally did not represent clients on labour issues and that critics who sought to connect his work for Burson with the campaign were playing a “false game of gotcha”.

The Financial Times