Reason is Simple...If you want to deposit Sing Dollors, go Foreign banks because they need your money to lend it out.
If you want to deposit US Dollors, go Local banks because they also need your money to lend it out.
As the largest banks from US, do you think Citibank need to pay high interest for your US dollors?
It involves Premium Deposit which is For the sophisticated investor ONLYPremium Deposit
For the sophisticated investor
Place your deposit in two currencies of your choice
It gives you substantially higher interest rates than a regular fixed deposit
Choose tenures from one week (for foreign currency) to six months
https://www.citibank.com.sg/portal/citiwm_home_center.jsp?productID=InvestmentsDeposits&path=/sggcb/english//prod/det/id_pd.htm&frameset=centerFrameset&frameval1=wowWorkID&framevar1=workID