Warren Buffett's Berkshire Hathaway (BRK.A) (BRK.B)  has asked the Federal Reserve for permission to hold as much as 24.99% of American Express (AXP) , a stake that's been increasing because of the lender's stock buybacks, Bloomberg reports.

"This is an application to continue to retain American Express stock, not to buy additional shares," American Express spokeswoman Marina Norville said.

Berkshire applied to "increase the percentage ownership cap to 24.99% from the current 17% as a result of our share-repurchase program," she added.

The New York-based financial services firm has recently returned "significant amounts of capital to shareholders" through dividends and buybacks, CFO Jeffrey Campbell said on a conference call last month.

American Express won approval to repurchase $4.4 billion of its shares during 2016 and an additional $1.7 billion in the first half of 2017.

Shares of American Express are higher in late morning trading.

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