Royal Bank of Scotland is keen to proceed with an initial public offering (IPO) of its US subsidiary, Citizens, more quickly than originally envisaged, if market conditions are right, sources have told Reuters.In February the troubled British lender said that it planned to sell between 20% and 25% of Citizens by the end of 2014 via a New York IPO. The bank is under pressure from regulators to buttress its capital and at least a few analysts - who have valued the unit at between $9bn and $15bn - have suggested that selling its US arm might be the easiest source of new funds. RBS, however, is thought to be wary of being pressured into selling at knock-down prices. The lender is expected to name Morgan Stanley as the lead underwriter for a proposed initial public offering, Reuters reported citing people familiar with the matter.At 09:51 shares of RBS rose 1.85% to 363.11p. AB