UPDATE 1-Office Depot posts surprise loss, shares plunge

(Adds details, background, analysts' estimates, shares)

Feb 25 (Reuters) - Office supply retailer Office Depot Inc reported a surprise quarterly loss as same-store retail sales fell 4 percent in North America, sending its shares reeling.

Office Depot shares fell about 15 percent in premarket trading on Tuesday, while those of rival Staples Inc dropped 2.5 percent.

Office Depot, which acquired OfficeMax in November, said its fourth-quarter net loss widened to $144 million, or 34 cents per share, in the quarter ended Dec. 28 from $17 million, or 6 cents per share, a year earlier.

The results include acquisition-related charges of more than $100 million.

On an adjusted basis, Office Depot reported a loss of 3 cents per share. Analysts on average had expected a profit of 3 cents per share, according to Thomson Reuters I/B/E/S.

Sales rose 33 percent to $3.49 billion but fell short of the average analyst estimate of $4.03 billion. Sales included $939 million from OfficeMax.

About 40 percent of the company's sales came from its North American retail business. North America business solutions division contributed about 34 percent of revenue.

Office Depot also has an international division.

Decreased store traffic resulted in fewer transactions in the North America retail business, the company said. The average order value also fell.

Office supply retailers have been struggling as more shoppers buy their paper and gadgets from e-retailers such as Amazon.com Inc as well as drugstores or mass merchants.

Office Depot forecast 2014 sales to be lower than pro-forma combined sales in 2013 and said it expected to generate adjusted operating income of at least $140 million.

The company, which appointed turnaround expert Roland Smith as chief executive in November, said it expects $400 million of integration expenses between 2014 and 2016. About $300 million would be incurred in 2014.

Office Depot's $976 million acquisition of OfficeMax, announced last February, was aimed at cutting costs, consolidating stores and improving chances of fighting off market leader Staples and online and discount rivals.

Office Depot shares rose 27 percent in the year to Monday's close of $5.35 on the New York Stock Exchange. Staples shares rose less than 1 percent in the same period.

(Reporting by Maria Ajit Thomas in Bangalore; Editing by Joyjeet Das; Editing by Joyjeet Das)