For the ECB, one of the most pressing issues may be the investor flight to top-rated government debt seen since the referendum, which reduces the availability of bonds to purchase as part of its 1.74 trillion euro quantitative easing scheme.
Nearly a third of euro zone government bonds are no longer eligible for the asset buying scheme because they yield less than the bank's minus 0.4 percent deposit rate, according to Tradeweb data on Thursday.
The ECB said a remark had been made at the June meeting that markets see a future challenge in sourcing sufficient volumes of debt to buy, possibly leading to increased price volatility.
Although the ECB can substitute assets if it cannot buy enough government debt, investors remain closely tied to specific market segments, so the actual composition of purchases still matters, the ECB added.
Some analysts predict the bank will not have enough German, Irish and Portuguese bonds to buy due to its self-imposed limits, forcing the ECB to tweak some of its rules if it wants to maintain monthly purchases at 80 billion euros per month until March, when the scheme is due to run out.
Any extension of the purchase program, expected by many analysts and investors, would almost certainly require changes either in the self-imposed limits or the types of assets the bank can buy.
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