Citigroup Inc has increased interest rates on up to 15 million U.S. credit card accounts just months before curbs on such rises come into effect, the Financial Times reported citing people close to the situation.

Citigroup had upped rates on 13 million to 15 million credit cards it co-brands with retailers such as Sears, the paper said.

In a statement, Citigroup said "We have adjusted pricing and card terms for some customers as part of our regular account reviews. This is an ongoing process to ensure we offer terms, interest rates, credit lines and products based on individual needs and risk profiles."

"These changes also reflect the dramatically higher cost of doing business in our industry as we work to preserve the broad availability of credit," Citigroup told the paper.

Citigroup could not be immediately reached for a comment by Reuters.