Sears Holdings is closing an additional 20 money-losing stores, a sign of the mounting problems faced by the iconic but troubled retailer.

The move includes 18 Sears stores and two Kmart stores. The plan was disclosed early Friday in a filing by Seritage Growth Properties (SRG), the landlord for more than 200 Sears and Kmart properties.

"Sears Holdings continues to actively manage our real estate portfolio to identify additional opportunities for reconfiguration and reduction of capital obligations," Sears said in a statement. It said it will begin liquidation sales next weekend and that the stores are expected to close by mid-September. The company did not give details as to which stores are closing.

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The 20 closings bring the company's total so far this year to 236, or roughly 17% of the stores it had in January. In addition, it shut down pharmacy operations at 92 Kmart stores as well as Sears Auto operations at 50 stores, although it kept the stores at those locations open. Sears closed 240 stores last year and 53 in 2015.

Sears warned in March that there is "substantial doubt" about its ability to remain in business due to losses that have topped $10 billion since 2010, the last time it turned a profit.

Sears is hardly the only retailer shuttering locations. There have been about 5,300 store closing announcements so far this year, according to Fung Global Retail & Technology, a retail think tank.

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On Thursday, Sears Canada, a separate company that Sears spun off in 2012, filed for bankruptcy protection. It said it plans to close 59 of its more than 200 stores, and to lay off 2,900 of its 17,000 employees as part of its restructuring efforts. Sears Holdings owns about 12% of Sears Canada, while Sears CEO Eddie Lampert owns about 45% of its shares both personally and through his hedge fund.

Seritage is a real estate company that was created by Lampert in 2015 in order to buy Sears Holdings (SHLD) properties and then lease them back to the retailer to free up cash. Lampert is chairman of both Sears and Seritage.