MADRID--Spain's "bad bank" is set to change how it markets and sells around EUR50 billion ($68.5 billion) worth of properties and real-estate loans, a move that could open the door for international investment funds to deepen their involvement in the country's real-estate market.

No more than four investment firms will be selected in coming months to market and sell the pile of properties and real-estate loans held by the bad bank, according to an executive at the company, known by its Spanish acronym Sareb. The executive declined to be named. Sareb recently said it made a loss of EUR261 million last year.

The bad bank was created in November 2012 as a depository for the most troubled Spanish banks to unload EUR51 billion in risky real-estate loans, residential foreclosures, unfinished commercial properties and undeveloped pieces of land.

The country's lenders transferred nearly 200,000 real-estate related assets to the bad bank. Now, the nine banks that unloaded those assets to Sareb also market and sell the properties and loans on behalf of the bad bank. Sareb paid those banks--including Bankia SA, the country's largest bailed-out lender--EUR200 million in fees to sell properties last year. The new servicers will be selected based on price and experience, the executive added.

The current set-up creates a potential conflict of interest, the executive said, since the banks that are managing Sareb's assets are also trying to unload their own real-estate assets that weren't transferred to Sareb. The contract with those nine banks ends December 2014.

Sareb will launch a bidding process in coming weeks to find firms to replace the banks, the bad-bank executive said, and a winner will be named before September. New servicing contracts would resolve that potential conflict of interest, he added.

Fifty-five% of Sareb is privately held by most of Spain's major banks, such as Banco Santander SA and Caixabank SA. Those shareholder banks offer mortgage deals to clients who purchase homes sold by the bad bank, which Sareb says helps it sell more properties while bringing the banks new clients. Some analysts have said it is a potential conflict of interest that Spain's biggest banks--that are also trying to sell off thousands of properties--are on the board of the bad bank. Sareb says it manages those potential conflicts of interest through strict rules about who can know about and participate in board votes.

The remainder of Sareb's shares are held by Spain's bank restructuring fund, known by its Spanish acronym Frob.

The shake-up of Sareb's marketing and sales process comes as international investors have stepped up their presence in Spain's property market through purchases of banks' real-estate servicing units. Banco Santander, Spain's largest banking group, sold its Altamira unit to Apollo Global Management LLC in January while Caixabank SA, Banco Popular Español SA and Bankia have also recently sold their real-estate-servicing units.

Sareb has sold an average of 60 homes a day since the beginning of the year--a pace that could slow, the bad bank executive cautioned. That is up from a daily average of 25 homes last year and above the bad bank's goal of an average of 30 a day for 2014.

Eighty per cent of Sareb's portfolio is loans to real-estate developers, the executive said. The remainder is residential homes, land and commercial properties. The bad bank is also planning to hire construction firms to start building on some of the empty plots of land in the hopes of increasing the sale prices of those plots, he added.

The bidding process comes amid a personnel shift at Sareb. Jaime Echegoyen, the former head of Barclays PLC's retail banking unit in Spain, took over as the chief executive of the bad bank in February. Before Barclays, Mr. Echegoyen was chief executive of Bankinter SA, Spain's sixth-largest bank by market capitalization.

The European Union required the creation of Sareb as a condition for Spain to receive EUR41 billion in bailout funds after a property boom-and-bust threatened to bankrupt Bankia and other lenders.

The International Monetary Fund said in a February report about Spain's financial sector that Sareb must "devise and implement effective liquidation strategies geared toward supporting its cash flow and profitability, and adjusting nimbly to changing macro and market conditions."

Write to Jeannette Neumann at jeannette.neumann@wsj.com

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