Federal bank regulators are warning consumers against proliferating scams involving fraudulent cashier's checks that can cost them thousands of dollars.

The Office of the Comptroller of the Currency, the Treasury Department agency that oversees nationally chartered banks, issued a consumer advisory Tuesday on the scams. Typically, people usually receive a cashier's check in the mail and are asked to deposit it in their bank account, wait until funds become available and then wire a portion of the money from their account to a third party — often in a foreign country.

Cashier's checks, widely used for decades, are issued by banks and other financial institutions and are drawn on the institution's funds rather than those of the depositor. That means the amount of a cashier's check quickly becomes available for withdrawal by the person to whom it is written after the check is deposited — but not if a check is fraudulent. It may take weeks to discover that a check is bogus and the person targeted in a scam may have already wired the money to those requesting it or otherwise used it, the regulators said. When the fraud is eventually detected, the consumer may discover that he owes the full amount of the cashier's check deposited in his account.

The incidence of the scams, many involving a phony unexpected windfall for the consumer, has been rising in the last year or so, the comptroller's office said. A spokesman said figures were not available for losses to consumers or the number of scams discovered.

In one widespread scam, the consumer is notified that he has won a lottery in a foreign country and that the proceeds will be sent to him after the required taxes or fees are paid. A bogus cashier's check is provided to purportedly cover those charges and the consumer is asked to deposit it in his account, wait until it clears and then make a wire transfer of funds — often to a foreign bank — to cover the taxes or fees.

"Cashier's checks serve an important purpose in the financial marketplace, but we are starting to see an increasing number of scams involving these instruments," Comptroller John Dugan said in a statement. "In most cases, consumers can avoid becoming victims by remembering that if something sounds too good to be true, it probably is."

Although the amount of the cashier's check may be available to the consumer the next business day, the availability of funds — sometimes referred to as a check clearing — does not necessarily mean that the check is legitimate, the comptroller's office said. It may take several weeks for a fraudulent check to be detected and returned to the consumer's bank, which will then reverse the deposit and withdraw the equivalent amount from the consumer's account.

Wire transfers cannot be reversed or recovered by the bank.