CHICAGO (From news reports) -- R.R. Donnelley & Sons Co., the printing and information services company, said it received a higher non-binding offer from a strategic party just days after it agreed to be bought by Chatham Asset Management LLC.

The Chicago-based business got an unsolicited bid at $11 a share, Donnelley said in a statement late Wednesday, without identifying the party. That compares with the $10.85 a share deal with Chatham that ended a two-month bidding war with Atlas Holdings. Donnelley's board reaffirmed its recommendation of the Chatham merger agreement.

"At this time, the board has not determined that the strategic party proposal constitutes a superior proposal, and there can be no assurances that a transaction will result from the strategic party proposal or that any alternative transaction will be entered into or consummated," according to the statement.

The shares rose as much as 4.9% to $11.19 on Thursday morning. The stock has gained 372% this year.

This isn't the first time the mystery bidder has sought to upend Donnelley's deal talks. The company said in late November that it received a non-binding proposal from the strategic party at $10 a share in cash, subject to other terms and conditions. Both Atlas and Chatham then came in with higher bids.

Chatham is Donnelley's largest shareholder, with 15% of the stock. It also holds a substantial amount of its debt.

Donnelley, which was founded in 1864, is a global provider of business services such as printing, packaging and direct mail. The company said it has roughly 30,000 clients and 33,000 employees across 28 countries. Net income last year came to $98.5 million on sales of $4.8 billion.