NEW YORK — CitiFinancial, the consumer finance division of Citigroup Inc., announced Monday that it has begun notifying some 3.9 million U.S. customers that computer tapes containing information about their accounts have been lost.

Citigroup, which is based in New York, said the tapes were lost by a courier in transit to a credit bureau.

The bank said the tapes contained information about both active and closed accounts at CitiFinancial's branch network. It said they did not contain information from CitiFinancial Auto, CitiFinancial Mortgage or any other Citigroup business.

The statement said that CitiFinancial "had no reason to believe that this information has been used inappropriately, nor has it received any reports of unauthorized activity."

It was the latest in a series of data losses or breaches that have forced financial institutions and other data collectors to warn customers that their personal information may be at risk.

Last month, media and entertainment company Time Warner Inc. said that computer backup tapes containing data on 600,000 individuals were lost by an outside data storage firm.

The data were on current and former employees going back to 1986, as well as some of their dependents and beneficiaries, the company said. It did not include personal data on Time Warner customers, the company said.

Also in May, more than 100,000 customers of Wachovia Corp. and Bank of America Corp., both headquartered in Charlotte, N.C., were notified that their financial records may have been stolen by bank employees and sold to collection agencies.

In all, nearly 700,000 customers of four banks may be affected, according to police in Hackensack, N.J., where the investigation was centered.

CitiFinancial issued an apology for the latest data loss.

"We deeply regret this incident, which occurred in spite of the enhanced security procedures we require of our couriers," said Kevin Kessinger, executive vice president of Citigroup's Global Consumer Group and president of Consumer Finance North America. "There is little risk of the accounts being compromised because customers have already received their loans, and no additional credit may be obtained from CitiFinancial without prior approval of our customers."

Kessinger said that beginning in July, the data "will be sent electronically in encrypted form."

Citigroup shares fell 11 cents to $47.45 US in midday trading on the New York Stock Exchange.