Andrew Thursfield, head of Citigroup's European risk treasury business, told the jury in the trial of former trader Tom Hayes that the U.S.-based bank had been able to borrow at rates below those posted on trading screens by brokerages.

Thursfield, appearing as a witness for the prosecution, said broker screens were showing Libor rates that the U.S. bank felt did not reflect the full range and width of the market.

In an email exchange with U.S. colleague Scott Bere on Sept. 7 2007 that was shown to the court, Thursfield said: "We will continue to pressure the brokers to talk it (Libor) down and generally press lower than all others...".

Thursfield is a Citigroup veteran who has spent more than 20 years in the bank's treasury department.

Hayes, a former Tokyo-based yen derivatives trader, is charged by Britain's Serious Fraud Office (SFO) with eight counts of conspiracy to defraud between 2006 and 2010.

Hayes, who allegedly tried to rig rates to benefit his trading book, has pleaded not guilty and is expected to lay out his defence next month in a trial scheduled to last well into August.

Hayes, a 35-year-old Briton, who worked for Citigroup in 2010, is accused of using a network of traders and London brokers to influence the yen denominated London interbank offered rate (Libor), used as a reference for around $450 trillion (£286 trillion) of financial contracts worldwide.

Bere, head of Citigroup's North American risk treasury business, whose emails were also shown to the jury and read out in court, wrote to Thursfield on Sept. 13, 2007: "Assuming you don't need a high setting for your book ... I would appreciate it if we could be aggressive with our setting (ie 60 or lower)."

Thursfield told the court that the beginning of that email did not really make sense to him as banks were not allowed to take their trading books into account when setting Libor rates. Libor rates are designed to reflect interbank borrowing costs.

But he said under questioning by the prosecution that the email was ambiguous.

Thursfield told the court he gave "general guidance" to the people who submitted Citigroup's Libor rates and said the bank never "lowballed" the rates during the credit crisis to flatter perceptions of its creditworthiness.

(Editing by Jane Merriman)

By Kirstin Ridley