American International Group Inc.'s Japan arm, at the center of the country's worst fiasco involving fraudulent use of credit cards, admitted Wednesday that 230,000 of its card-holding customers may have had their data leaked to unauthorized outsiders and a Chinese service provider may be involved.

The significant leap from the 18,000 cases announced by Alico Japan in September came to light after the insurer expanded the scope of its internal investigation to other types of credit cards that were not subject to an earlier probe, company officials said in Tokyo.

Alico Japan said confirmed data leak cases numbered 32,359. In September, 18,184 were announced.