For the second time in three months, speculation is swirling that the ailing Royal Bank of Scotland may have to sell its US subsidiary, Citizens Financial Group, to raise money.

The latest rumors have been fueled by reports that the British bank’s chief regulator urged RBS chief Stephen Hester in a recent letter to consider selling Citizens, which has its headquarters in Providence. The British government, which bailed out the bank during the financial crisis, still has about an 81 percent ownership stake and would eventually like to be repaid.