DUBAI (Zawya Dow Jones) -- Mideast sovereign wealth funds may fail to save troubled U.S. banking giant Citigroup Inc. unless more cash is pumped into the lender, the head of a $13 billion Dubai-owned investment firm said Tuesday.

Sameer Al Ansari, Chief Executive of Dubai International Capital told delegates at a private equity conference that it will take more than the combined efforts of the Abu Dhabi Investment Authority, the Kuwait Investment Authority and Saudi investor Prince Alwaleed bin Talal to save the bank.

"It's going to take more than that to rescue Citi," Ansari said. He added that more write downs are expected and that Gulf investors would be required to bolster Citi.

The Abu Dhabi Investment Authority, or ADIA, a sovereign wealth fund owned by the world's fourth-largest oil exporter, last year bought a 4.9% stake in Citigroup.

The Kuwait Investment Authority also said in January it would invest $3 billion in Citigroup.

Al Ansari said "it would take a lot more money to rescue Citigroup." A spokesperson for Citi was unable to comment immediately when called Tuesday.