The ECB will intervene to stem liquidity crises that affect European banks' stability and to maintain midterm price stability, but large-scale sovereign bond buying remains "well beyond" its role as lender of last resort, governing council member Christian Noyer said.
The Bank of France governor said restoring market confidence in the euro zone would likely be a "difficult and potentially lengthy task," but he added that timely implementation of fiscal and structural economic reforms by eurozone governments was necessary.
"Engaging in large scale purchases of sovereign bonds is well beyond what should be expected in the central bank's role as a lender of last resort," Noyer told a conference in Paris.
He said that measures announced earlier this month to furnish unlimited 36-month funds to euro zone banks while easing collateral requirements was aimed at stabilising the liquidity of the banking system and the operation of money markets to allow credit to flow to the real economy.
The euro zone crisis was easing inflationary pressures in the 17-nation bloc, Noyer said, adding that policymakers found themselves in a particularly challenging environment where unconventional measures were necessary.
"The best possible contribution of the euro system is to ensure price stability in the medium run," the French central banker said.
"To the extent that financial markets jeopardize price stability, the euro system must intervene. This analysis has motivated our decisions in the past and will continue to motivate them."
While he acknowledged that sovereign yields were "central" to European credit markets, he said that the European Central Bank should not rush into measures such as large-scale government bond buying which might bring short-term benefits but carry onerous long-term consequences.
"Large scale asset purchases are not without risks. Although they may help to eliminate upward pressure on interest rates in the short term, they will also affect price and financial stability in the medium run," he said.
"Such risks will not necessarily materialise, but when they do the repercussions are immense," he added.