DUBAI, April 28 (Reuters) - Saudi Tadawul Group, the owner and operator of the country’s stock market, said on Wednesday it appointed JP Morgan, Citigroup and the securities arm of Saudi National Bank for its initial public offering. Tadawul said the public share-sale will allow it to expand and strengthen its position globally. The deal is part of efforts by Saudi Arabia to diversify its economy. (Reporting by Hadeel Al Sayegh. Editing by Jane Merriman)