By John Spence

BOSTON (Dow Jones) -- Shares of real-estate investment trusts traded lower Monday as disappointing corporate news from the sector fed concerns that the credit crunch and a slowing economy will continue to weigh on owners of commercial properties.

Troubled mall developer General Growth Properties Inc. (GGP) said it hasn't yet been able to reach a deal with its lenders to further extend the maturity date on $900 million in mortgage loans.

Also Monday, Developers Diversified Realty Corp. (DDR) said a previously announced deal to sell assets to a joint venture with an institutional investor would not close in December as had been expected.

Shares of Developers Diversified and General Growth were both down more than 10% Monday morning. ProLogis (PLD) was another big percentage decliner in the REIT sector and was off about 10%.

The SPDR Dow Jones Wilshire REIT ETF (RWR) had lost about 2% at last check. The ETF is down by roughly half so far in 2008 in what has been a tough year for commercial real estate. REITs with higher leverage and big debt repayments coming due have been among the hardest-hit.

General Growth said Monday that it had not reached unanimous agreement with its lenders to further extend the maturity date on $900 million of mortgage loans on two Las Vegas properties. The shopping-mall owner and operator said it's continuing discussions with lenders regarding its loans.

General Growth shares rallied 25% Friday after the company said it had refinanced nearly $900 million of debt. However, the company said the refinanced loans were separate from the mortgage loans related to Fashion Show and Palazzo -- the two malls in Las Vegas -- that were set to mature Friday.

Meanwhile, Developers Diversified on Monday said an agreement to sell assets to a joint venture wouldn't close this month as planned.

The shopping-center operator said it "continues to engage in active discussions with the institutional investor concerning assets which might be included in a potential transaction in 2009."

Developers Diversified said it expected to maintain compliance with all loan covenants and sufficient liquidity to meet all near-term liabilities, and it added that it continues to "actively pursue" further asset sales and additional financing alternatives with numerous potential sources.

"We are disappointed to not close on the large joint venture as we had expected, but we continue to access many sources of capital in order to meet our goals of improving our liquidity and lowering our leverage," said Chief Investment Officer David Oakes in a written statement.

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