(Adds details, updates shares)
April 4 (Reuters) - Staples Inc is considering selling itself, and is in talks with private-equity bidders, a source familiar with the matter said on Tuesday, sending the largest U.S. office supplies retailer's shares up about 15 percent.
The retailer last year called off a proposed merger with rival Office Depot Inc due to antitrust concerns.
Both companies have since announced cost-cutting plans and sold most of their European operations to focus on their North America businesses.
Framingham, Massachusetts-based Staples had a market value of $5.65 billion as of Monday.
Staples has reported falling sales for the last five years as it faces growing competition from Amazon.com and other online sellers, as well as big-box retailers such as Costco Wholesale Corp and Wal-Mart Stores Inc.
Staples spokesman Mark Cautela declined to comment.
Office Depot's shares rose about 5.3 percent to $4.94 in morning trade.
The Wall Street Journal reported earlier that Staples was exploring a sale. (Reporting by Sruthi Ramakrishnan in Bengaluru and Lauren Hirsch in New York; Editing by Sai Sachin Ravikumar and Martina D'Couto)