Citi has rejected a lawsuit by former Singapore private banking client claiming that he lost more than $1 billion as a result of the bank providing inaccurate information and failing to execute some of his trades, Reuters reports.

In the aftermath of the financial crisis - and the bankruptcy of structured products manufacturer Lehman Brothers in particular - many private banking clients have been left nursing huge losses. A number of such clients have commenced legal action against the institutions that advised them, with allegations of poor advice, inadequate due diligence and the mis-selling of investment products being recurring themes in these suits.

As previously reported, Oei Hong Leong sued Citi last month for negligence and misrepresentation, alleging that the bank failed to execute $600 million worth of buy orders for US Treasuries. Mr Oei, who is known as one of Singapore’s wealthiest businessmen, also accused Citi of having painted an inaccurate picture of his trading exposure, leading him to take on more positions than he would otherwise have done.

In a court filing seen by the news agency, Citi said Mr Oei had "demonstrated a considerable appetite for risk and an understanding of the risk and exposure associated with the various derivative investment structures entered into." At one point, in February 2008, his open positions with Citi reached $6.89 billion, the bank said.

Citi said it had not executed Mr Oei’s buy order for US treasuries because he had consistently set his price limit beneath indicative market prices and vehemently denied allegations it had supplied inaccurate and misleading margin numbers.

Mr Oei’s claims of a "meltdown" in Citi’s tracking and control systems were slammed by the bank as "contrived afterthoughts."

"We intend to vigorously defend the action. We have today filed our defence," Citi's private bank said in a statement on Friday.

Mr Oei’s lawyer, Quek Mong Hua, is quoted as having said Citi’s denial "was not unexpected" and that his team were studying Citi’s defence.