Royal Bank of Scotland's (RBS) shares rose following reports that Japan's Sumitomo Mitsui Financial Group may bid for the lender's US retail banking division.The two banks met recently to negotiate a possible deal for RBS Citizens Financial Group, according to The Wall Street Journal which cited sources.In January the British bank said it was open to takeover offers of Citizens as it prepares the unit for an initial public offering (IPO) this year.On Tuesday, RBS spokeswoman Debbie Phillips said in a statement: "We announced in November 2013 that we would accelerate the IPO of Citizens, aiming to start the process in the second half of 2014 and to fully sell the business by the end of 2016," RBS spokeswoman Debbie Phillips said in a statement today. "That is our plan."Shares rose 1.28% to 307.50p at 10:00 on Tuesday.RD