FRANKFURT/MADRID (Reuters) - Banks such as Deutsche Bank (>> Deutsche Bank AG) and JPMorgan (>> JPMorgan Chase & Co.) are teaming up with international funds to bid for a multi-billion-euro portfolio of Spanish property loans as the country's real estate market thaws, sources close to the process said.

The loan package of over 4 billion euros ($5.5 billion), from Germany's Commerzbank (>> Commerzbank AG), is one of the biggest of its kind to be auctioned in Spain's six-year real estate slump as lenders burned in the crisis clean up their books.

It is made up of some soured debts and other performing loans backed by office blocks and shopping centers, rather than debts related to residential homes which have more commonly been offered to investors.

That is helping the portfolio attract buyers, the sources familiar with the process said, though funds have also been flocking to Spain recently as the country emerges from recession and property prices come closer to hitting bottom after falling around 40 percent since 2007.

Banks have been joining up with funds to bid together for the Commerzbank portfolio, and would most likely split the assets afterwards, with banks keeping the performing ones.

U.S. private equity firm Lone Star is bidding with JPMorgan for the loans, while Blackstone is working with Deutsche Bank, two sources familiar with those offers said. Apollo Global Managament (>> Apollo Global Management LLC) has put in a joint offer with Spain's Santander (>> Banco Santander, S.A.), a third source said.

U.S. private equity firm Cerberus has also put in a bid, two other people said, as has Oaktree Capital Group, according to a sixth source, though it was unclear whether these investors had bank partners.

Commerzbank, and the banks and funds declined to comment, as did Lazard which is handling the auction. Over 10 parties have put in bids, which were due at the end of last week, the sources said. Another round of bids is scheduled for April.

"Bidders can put in offers for the whole package, or just the parts they're interested in, such as the non-performing loans for example," said a real estate adviser close to the auction, which is known as "Project Octopus."

The portfolio includes 3.3 billion euros in performing loans and roughly 1 billion in non-performing loans, people familiar with the transaction have previously said.

A lawyer familiar with the process added that the deal could come with a small real estate management platform and a team of people to handle the debts.

International funds have been chasing these kinds of assets in Spain so they can build up credit management units and buy more loan portfolios. Apollo recently bought 85 percent of Santander's property management division, while bailed-out lender Bankia (>> Bankia SA) transferred the management of its platform to Cerberus for the next 10 years.

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Commerzbank, which was rescued by the state during the financial crisis, has been one of the biggest bank sellers of soured debts in recent months, in part as it gets ready for a Europe review of banking assets this year and frees up capital.

It is winding down a mortgage unit previously known as Eurohypo, and last July it sold British property loans worth 5 billion euros to U.S. lender Wells Fargo (>> Wells Fargo & Co) and Lone Star.

In February it already sold around $1 billion in bad Spanish property debts.

Real estate experts and other people close to "Project Octopus" said the sale could clear the way for more foreign lenders to offload Spanish real estate loans they were lumbered with after the 2008 market crash.

"The Commerzbank deal is so big that other banks keen to sell portfolios have been holding off, waiting for this to get done, as the bidders can't really focus on anything else right now," the lawyer familiar with the process said.

The prices paid for such assets vary enormously. Investors sometimes bid as little as five to 10 percent of the face value of distressed property loans, while better assets might be sold for 80 or 90 percent of face value.

Spanish lenders and foreign banks operating in the country had been slow to shed property portfolios until recently because the bid and ask price gap was very wide.

But the improving economy is encouraging investors to raise offers while banks have also taken hefty writedowns on the value of their loans and properties.

International funds, including big name investors such as U.S. billionaire financier George Soros, have also started to put money into other recovering sectors in Spain.

Soros took part in Spain's sell-down of a stake in Bankia, and also bought shares in builder FCC (>> Fomento de Construcciones y Contratas SA).

($1 = 0.7277 euros)

(Additional reporting by Freya Berry in London, editing by William Hardy)

By Arno Schuetze, Sarah White and Alexander Hübner