U.S. commercial real estate prices fell further in May, exacerbating problems for banks and other lenders holding risky loans.

Commercial real estate prices fell 7.6% in May, according to Moody’s. The rating agency’s gauge of commercial real estate – its commercial property indices – are off 28.5% from a year ago and they are down 34.8% from a peak in prices measured in October 2007.

In addition to a drop in prices, Moody’s said on Monday that sales volume by dollar amount and count fell to new historic lows in May.

A large part of the drop in sales comes amid a drought in credit. No new commercial mortgage-backed securities have been priced this year and this has prompted many lenders to close their doors. The decline in the number of lenders has also made it tougher for many borrowers to refinance their commercial real estate mortgages.

Separately, Standard & Poor's said on Monday that delinquencies of commercial mortgage-backed debt rose in June. Delinquencies in June hit 3.95%, up from 2.60% in May.

Much of the jump in delinquencies is tied to problems in the retail sector, specifically problems associated with the bankruptcy of General Growth Properties, a real estate investment trust that filed for bankruptcy in April. GGP borrowed to buy mall properties and refinanced loans for them, and a big slice of this debt was resold through securitization.