Overnight borrowing from the European Central Bank rose to a three-month high on Wednesday in a second day running of elevated lending in a market watched closely for signs of renewed banking stress.

Money market traders said with banks due to receive 155.2 billion euros (199.84 billion) in new weekly funds from the ECB on Wednesday, the increase probably meant someone had just miscalculated liquidity needs.

But if borrowing remained high for a third day, this could signal a bank was in trouble rather than a technical problem.

"Today the new weekly allotment goes in and that should sort it out," one trader at a euro zone bank said.

"We don't think it's anything too alarming, it could be due to a lack of collateral in the weekly operation," another trader said.

Tullett Prebon G-7 economist Lena Komileva said the borrowing spike reinforced the argument for the ECB to extend its policy of offering banks unlimited funds at its September meeting.

"There are still a large group of institutions which have struggled to pass the stress tests of open markets and are struggling to meet their structural liquidity needs," she said.