UBS, one of the biggest casualties of the US subprime turmoil, faces a shareholders' revolt over plans for a massive infusion of funds from Singapore and the Middle East to improve its capital ratios.

The move comes as the Financial Times learned that the mystery Middle Eastern investor ploughing SFr2bn ($1.73bn) into UBS's recapitalisation is from Saudi Arabia. "It's a reasonable assumption the ruling family was involved and approved [the deal]," said one figure with knowledge of the negotiations.