Greece’s credit rating was cut two levels to B from BB-minus by Standard & Poor’s, which said further reductions are possible, with private investors at risk if maturities are extended on the nation’s emergency-aid package.

Another cut would make Greece the lowest-rated country in Europe as today’s move left it even with Belarus after the fourth reduction by S&P since April 2010.

“The downgrade reflects our view of increasing sentiment among Greece’s key euro-zone official creditors to extend the debt payment maturities of their 80 billion euros ($115 billion) of bilateral loans pooled by the European Commission,” S&P said in an e-mailed statement. “As part of such an extension, we believe the euro-zone creditor governments would likely seek ‘comparability of treatment’ from commercial creditors in the form of their similarly extending bond and loan maturities.”

A year after Greece received a 110 billion-euro aid package that aimed to stem the spread of the region’s sovereign crisis, the nation’s debt is rising and it faces record borrowing costs. Its two-year bonds yield more than 25 percent, indicating investors are betting Greece won’t be able to return to markets as planned under the bailout next year, when it was due to sell 25 billion euros to 30 billion euros of bonds.

The difference in yields between Greece’s benchmark 10-year bond and comparable German debt increased 17 basis points to 12.5 percentage points today and the cost of insuring its debt against default reached a record 1,360 basis points.

The cut “comes at a time when there have been no new negative developments or decisions since the last rating action by the agency just over a month ago and therefore is not justified,” the Athens-based Finance Ministry said in an e- mailed statement today.