"Citigroup created havoc in European government bond markets," said Bertrand de Mazieres, the chief executive of the French Treasury on Monday.

"We told Citigroup that they had tarnished the image of European government bond markets and that this was regrettable."

The comments are the first public show of displeasure from a European treasury at Citigroup's actions, and the first concrete sign that the matter has impacted the bank's business prospects.

The trade prompted the French Treasury to lower Citigroup's position in its league table of primary debt dealers.

"Citigroup isn't at the level of the primary dealers ranking it should have been due to the August trading," Treasury Deputy Chief Executive Benoit Coeure said.

On-going investigation

Several European regulators are investigating Citigroup's 2 August rapid-fire sale of $16 billion of bonds on a range of electronic trading platforms.

The bank bought back $4.9 billion in bonds half an hour later.

German regulators say the bank also bought bond futures before the cash trade.

The Frankfurt state prosecutor is assessing whether six Citigroup employees involved in the trade are guilty of manipulating the market.