European Central Bank Governing Council member Joachim Nagel refused to exclude that interest-rate increases may persist beyond the summer.

Asked in a Bloomberg Television interview whether borrowing costs may still be rising in September, the Bundesbank president said “there’s nothing off the table.”

“Inflation is still very sticky,” Nagel said Thursday in Niigata, Japan, where he’s attending the meeting of Group of Seven finance chiefs. He described price gains as “a very stubborn phenomenon.”

The ECB is emphasizing that rates will increase more after it slowed the pace of its unprecedented tightening campaign last week. Most economists predict two more quarter-point steps to bring the deposit rate to a peak of 3.75% in July, though officials are starting to accept that hikes may be needed for longer, according to people familiar with the debate.

Nagel said borrowing costs are approaching levels that are restrictive for the 20-nation euro-zone economy, but aren’t there yet. Whether another move materializes in September will hinge on the impact of the 375 basis points of tightening to date.

Regardless of the outcome, Nagel said rates must remain high once they reach their peak.

“When there’s a point coming when we could more or less stop the rate hikes, then I have to believe that we have to stay there for a while,” he said. That would allow officials to “see if we’re really successful or not.”

--With assistance from Jana Randow.