The Financial Services Agency, the Japanese regulator, has started investigating a ¥1bn (€7.1m) trading error made at a Citigroup subsidiary in Tokyo this week. It is the second time the regulator has probed part of the US bank in less than 18 months.

A trader at Nikko Citigroup, the US group's investment banking joint venture with Nikko Cordial, intended to buy two shares in paper maker Nippon Paper at ¥502,000. The trade was made on his own account.