A Merrill spokesman in Hong Kong, Rob Stewart, said all of Mr Harjani's allegations are "without merit." Through a lawyer, Mr Harjani declined to comment. His lawyer said Merrill's actions in selling the shares had lost his client money.

The dispute is the latest example of the woes facing the world's big wealth managers in Asia. In the past few years, Wall Street's biggest names staffed-up in Asia to provide private-banking services to the newly rich.

But the fallout from the market downturn is raising increasing questions about how well the banks knew their clients and whether those clients were adequately warned about the investment risks.

Analysts warned even before the financial crisis reached its height that private banks and other wealth management firms faced rising risks of litigation from angry clients who have lost money.

Already, many Asian private-banking clients have complained about losses on so-called accumulators - essentially bundled derivative contracts that offer investors the ability to buy a security or currency at a fixed price over a period of time. The price usually represents a discount to the market, and as long as prices continue rising, the investor locks in tidy profits. When prices dive, as they have this year, the discount is wiped out, and the investor is unable to exit without incurring heavy losses.

An Indonesian couple is seeking $8.6 million in damages from UBS Singapore court, claiming they weren't aware of the risks involved in a currency accumulator that went bad. In Hong Kong, a local businesswoman, Joyce Tsang, is suing US investment and commercial bank Goldman Sachs for allegedly trading accumulators for her account without her authorization.

Goldman Sachs and UBS deny any wrongdoing.