"How we move in the future to zero, is actually a very minor issue in the context where the stock of accumulated purchases is already in the trillions of euros," Hansson told Reuters. "So the question about 10 billion euros there or the precise phasing, I think is not really a material issue."

Hansson added that bond purchases from the private sector will remain substantial next year even when government bond buys are cut, so the share of covered and corporate bond buys could even grow as a portion of all asset purchases.

"I don't think anyone is talking about ramping up (private sector buys), so it is just maintaining the significant purchases and therefore the share of the private sector element can grow," Hansson said on the sidelines of a news conference.