FRANKFURT, Germany (AP) _ The European Central Bank left its key interest rates unchanged following its regular meeting Thursday, despite speculation that an increase is coming.

The bank left its main refinancing rate at 2.5 percent, where it has been since a 0.5 percent cut in April.

Bank president Wim Duisenberg indicated then that the reduction would be the only change for the year. But after bank officials last week signaled they were starting to worry about the risk of inflation, many economists said chances were good the bank's governing council would raise rates.

Manuela Preuschl, an economist with Deutsche Bank in Frankfurt, said she believed an increase to 3 percent was possible later in October or November.

``A rate rise is really only a question of timing,'' she said.

The bank also confirmed Thursday that its overnight deposit rate will remain at 1.5 percent and its marginal lending rate will continue to be 3.5 percent.

The rates apply mainly to loans involving large financial institutions but changes in those rates can trigger changes in commercial and consumer lending rates.