Royal Bank of Scotland has announced the pricing of the $3.4bn flotation of its US arm Citizens Financial Group.RBS said it planned to sell a quarter of the shares in Citizens at $21.50 per share and a further 3.75% in an over-allotment option, raising up to $3.46bn more.The offer comprises 140m shares and the over-allotment option would include another 21m shares.RBS will continue to hold up to 75% of Citizens' shares, or 71.25% if the over-allotment option is exercised in full. Trading in the shares will start on Wednesday on the New York Stock Exchange.RBS, which is 81% owned by the British government following its taxpayer bailout in the financial crisis, is selling Citizens and other operations as part of a turnaround drive to restore the bank's finances and prepare it for an eventual return to the private sector.RBS chief executive Ross McEwan said: "The sale of Citizens is an integral part of the RBS capital plan. This IPO represents a key step on the path to full divestment. Selling Citizens will significantly improve our capital position and help us to create a strong and secure bank."