US banking giant Citigroup's legal spend rose by 33% in the first quarter of 2014.

The figures, contained in the bank's financial report for the first three months of the year, show operating expenses including $945m (£565m) in legal and related costs, compared with $710m (£425m) for the equivalent period last year.

Legal costs are up 17% on the last quarter of 2013, when it spent $809m (£484m).

The report states that its operating expenses of $12.1bn for the quarter were 1% lower than Q1 2013 as a result of efficiency savings and the overall decline in Citi Holdings assets, but that these were "partially offset by higher regulatory and compliance costs, legal and related expenses and repositioning charges in the current quarter".

The news comes as the bank reportedly faces investigations over fraudulent activity in relation to its Banco Nacional de Mexico operation, also known as Banamex.

Citigroup is among the host of banks accused of rigging rates in the foreign exchange market. It emerged last month that Covington & Burling is representing Citigroup.

Other firms landing major advisory roles on the scandal include Allen & Overy, which is acting for BNP Paribas, Davis Polk & Wardwell for the Royal Bank of Scotland and Sullivan & Cromwell for Barclays.

The bank's overall revenue for the first three months of the year has dropped 2% to $20.1bn (£12bn). However, quarterly profit rose by roughly 4% to $4.1bn (£2.45bn).