Some have argued that with the economy on more solid footing, the ECB could soon eliminate the punitive interest rate charge, raising the deposit rate to zero, even as asset buys continue.

“That would be a communication nightmare,” one of the sources said. “If you raise rates, you can’t communicate that it’s a one off, only back to zero, then we stop again.”

“The market would immediately price in a new rate path, pushing the entire curve sharply higher,” the source added.

With the euro zone government debt at 91.3 percent of GDP, not far below the 94.5 percent peak in 2014, governments can hardly afford big rise in borrowing costs as a yield rise could cap public spending, thwarting investment and growth.

The sources also argued that the market may not be accurately pricing risks related to the new U.S. administration, like the possibility of trade wars, protectionism, financial deregulation or President Donald Trump’s difficulty in pushing his agenda through Congress.

Banks, the biggest losers from negative rates, have meanwhile benefited from the steepening of the yield curve this year so there is no urgency to give them a hand, the sources added.

Inflation having hit 2 percent last month, essentially meeting the ECB’s target, also put some pressure on policymaker as German criticism of loose monetary policy heated up.

“Inflation has peaked for now and the oil price is down 10 percent so we are far having to worry about too much inflation,” a third source said.

While the sources acknowledged unexpected strength in the underlying economy, they said it was difficult to communicate this through its policy statements, especially with underlying inflation showing few signs of moving up.

“A small change in the wording can easily be blown out of proportion,” one of the sources said. “There is a communication risk and I would argue for stability.”