Spanish bond yields extended this week's rise before a debt auction where borrowing costs are set to stay high with the relief rally seen after last week's euro zone summit beginning to reverse.
The ECB announces its policy decision at 1145 GMT, with dismal economic data paving the way for the central bank to take its main refinancing rate down to just 0.75 percent .
"Every cut helps to a degree, but in terms of sovereign debt markets stabilising the question marks remain over last week's summit measures" said Brian Barry, fixed income strategist at Investec.
"Investors really at this stage of the game are moving towards some kind of fiscal integration or euro zone bond and we're still a way from any movement on that from the core countries."
The Bank of England is also expected to launch a third round of monetary stimulus.
September Bund futures were 27 ticks higher at 142.59, with 10-year yields down 1.5 basis points at 1.439 percent.
"Twenty-five basis points seems to be the consensus and there's probably going to be some disappointment if (the ECB) don't deliver," a trader said.
"Or perhaps the expectations just shift to next month. At the end of the day the data's not great, rates are staying lower for longer and there's not many reasons to sell Bunds."
SPAIN, IRELAND TEST PRIMARY MARKET
Spain will sell up to 3 billion euros of debt maturing in 2015, 2016 and 2022 with primary market dealers and domestic banks set to absorb the paper in the absence of international investors who have shunned the country's debt.
Borrowing costs are set to stay high despite euro zone leaders agreeing last week to allow the bloc's EFSF and ESM bailout funds to buy bonds in secondary markets and directly recapitalise ailing banks.
Spanish and Italian yields have reversed some of their post-summit falls with markets cautious given a lack of detail of how the plans will be implemented and with Finnish opposition dampening initial positive reactions.
And while some "fast money" accounts such as hedge funds piled into the market after the summit to close out their bets on the bonds falling further, traders consistently reported that they were not seeing any buying of the paper from longer-term investors.
"It feels like the forced buying, the short covering, we saw after the summit has been done now," the trader said.
"The auction should get done though, although we'll probably get a concession going into it."
Spanish 10-year yields were 12 basis points higher at 6.52 percent, with the Italian equivalent up 7 basis points at 5.82 percent.
Yields on Spain's 5-year October 2016 bond, which is being tapped on Thursday, were 18 basis points higher at 5.68 percent.
France will also sell 8 billion euros of longer-term bonds . Core paper is set to be well supported in coming sessions with almost 40 billion euros of German redemption and coupon payments hitting the market this week, followed by a further 50 billion euros of payments from triple-A rated countries, including France, next week, according to Reuters data.
Ireland - whose 5- and 10-year bond yields are currently below those of Spain - will return to the debt market for the first time since September 2010 with a sale of 500 million euros of 3-month bills.
Analysts are expecting yields of between 2- and 3 percent, while anything below 2 percent would be considered a success, said one.