Citigroup Inc (C.N) is looking for a buyer for its retail forex brokerage CitiFX Pro as part of efforts to streamline the banking world's biggest currency trading operation, a source familiar with the situation told Reuters on Tuesday.

Citi has cut staffing and computerized many elements of its currency business in recent years and market sources say it has aggressively rationalized its institutional client base in the prime broking space since the start of this year.

But the sale would come at a time when other banks are beginning to think about reinvesting in currency trading, drawn by an improvement in volumes and trading returns over the past year.

CitiFX Pro is the bank's easily accessible online forex trading service, offering professional individual traders and smaller institutional players access to 130-plus currency pairs on several platforms backed up by Citi infrastructure.

It is part of a sub-sector of the forex market whose reputation has taken a hammering since the collapse of a handful of businesses, and hefty losses for others, after the Swiss franc's surge in January.

New York-based Citi has pared back internationally in recent years, pulling out of retail banking in long-established markets such as Japan. Industry surveys continue to rank it as the single biggest banking player in the $5 trillion a day forex market.