A report by S&P's chief European economist and a colleague said 2017 was likely to mark the return of inflation in the euro zone, though core readings that strip out more volatile goods such as crude oil should remain subdued and give the ECB leeway to maintain support.
"The ECB could choose to look through the rise in energy inflation as temporary," the report said.
"Monetary policy is likely to remain accommodative until core inflation experiences a sustained adjustment of its path, probably not before 2018."
At its last policy meeting in December, the central bank cut its pro-stimulus bond purchase programme to 60 billion euros (51.83 billion pounds) a month from April from the current 80 billion euros but extended the scheme until the end of 2017 - three months longer than expected.
It also held its main refinancing rate at zero and its deposit rate at -0.4 percent. [L5N1E323H]
Since then - and following December's spike in inflation - some economists and policymakers, notably in Germany, have urged the ECB to raise interest rates.
S&P says reports of the kind published on Monday do not have a direct influence on its ratings but views on broad issues like ECB stimulus are often cited by its sovereign analysts in euro zone ratings decisions.
(Reporting by Marc Jones; editing by John Stonestreet)
