The US Securities Exchange Commission (SEC) has opened an investigation on Royal Bank of Scotland (RBS), Credit Suisse, and other banks over their handling of faulty mortgage loans, as reported by Financial Times, which cited sources close to the matter. The US regulator is studying whether these banks "misled shareholders about how many loans they might be forced to repurchase because of early defaults," the Financial Times reported.The "pink 'un" also reports that the SEC is investigating whether lenders had enough reserves to fund repurchases or handle related ligitation.At 11:45am, RBS is the best component on the FTSE100 with a 1.95% gain to 24.57 pence.SC