Nomura Holdings Inc., the nation's largest brokerage, may postpone an initial public offering of regional lender Ashikaga Holdings Co. by as much as two years, two sources said.

Nomura expects to sell shares in Ashikaga by March 31, 2013, two years later than originally planned, the sources said, declining to be identified as deliberations on the IPO are private. The Tokyo-based firm is Ashikaga's biggest shareholder, with a 46 percent stake.

The Topix Banks Index, which tracks 83 Japanese lenders, fell to the lowest since at least January 1983 on Thursday, almost a week after Mizuho Financial Group Inc. announced a plan to sell as many as 6 billion shares. That offering will add to more than $43 billion in stock sales by Mizuho and its two largest publicly traded rivals in the past two years.