Reuters reports that BNP Paribas said that the European Central Bank is likely to signal faster money printing on Thursday to keep a lid on borrowing costs but stop short of adding firepower to its already aggressive pandemic-fighting package.

The ECB cannot appear to micro-manage bond yields, since that would tie its hands in the future and invite accusations it is shielding governments from market forces.

The euro zone's central bank will also be keen not to overstate the rise in yields, which are still low by most standards. The German yield curve, the benchmark for the 19-country bloc, still in negative territory up to 20 years.

But having already committed to "maintaining favourable financing conditions", it cannot ignore even this modest rise in borrowing costs, as it has not been matched by improving economic prospects and mostly mirrors a move in U.S. Treasuries.

Another complication is that policymakers have already approved all the firepower needed to combat the rise in yields, so technically no new decision is required, since the bank still has a 1 trillion euro quota to buy bonds through next March.

But markets are now doubting the ECB's commitment. Purchase volumes have actually decreased in the past two weeks, confounding expectations it will use its much-emphasised "flexibility" to run up its bond-buying in line with a string of verbal warning from policymakers.