European Central Bank (ECB) policymakers have raised concerns that upbeat euro zone growth forecasts issued by their own staff may prove weaker than anticipated.

Separately, rating agency Standard & Poor’s has upgraded its economic outlook for the euro zone, suggesting cheap oil, a weak euro and the European Central Bank’s quantitative easing programme would underpin recovery.

Minutes from the ECB’s latest governing council meeting suggest while in-house economists broadly agreed with the positive outlook for the region’s economy some were sceptical.

In particular, several policymakers “remarked that the growth outlook for 2017 depended on a number of factors that might become less growth-supportive towards the end of the projection horizon”.

The ECB left its main interest rate at a record low just above zero at the off-base March meeting in Cyprus.

It also lifted its growth forecast for the euro zone economy to 1.5 per cent for this year, from the 1 per cent it predicted in December, and to 1.9 per cent in 2016, and 2.1 per cent in 2017, as the effects of its quantitative easing programme work through the system.

ECB staff foresaw euro zone inflation rising from 0 per cent this year to 1.8 per cent in 2017, which would put it in line with the bank’s target of close to but below 2 per cent.

Under its QE plan, the ECB aims to purchase €60 billion a month of mainly sovereign bonds until September 2016, or beyond that if needed to see a sustained adjustment in the inflation path back towards its target of just under 2 per cent.

ECB chief economist Peter Praet, who gave a presentation at the beginning of the meeting, saw no need for the Governing Council to reconsider any of the parameters around the programme, the minutes showed.

Council members “generally shared the assessment” that positive effects from the January 22nd decision to launch QE, along with previous policy stimulus, could already be seen in the easing of financial market conditions and lower financing costs.

However, Mr Praet said the council should “remain cautious” given the early stages of economic recovery in the euro zone.

Putting the onus on governments to do more to buoy the recovery, council members highlighted “the risk of insufficient progress on structural reforms ... as a major downside risk.”

In a thinly veiled jibe at a decision by European Union finance ministers last month to give France two more years to cut its deficit to the EU's limit, the ECB said in the minutes that "concerns were expressed about a tendency in recent decisions to ... use flexibility to the maximum extent".

Policymakers also flagged the possibility that a rebound in oil prices could weaken growth.

Conversely, in a research note, Standard & Poor’s said it had become more optimistic about the euro area’s economic outlook over the next two years than it had been in the final quarter of last year.

“Our view of the eurozone’s economic prospects for the coming two years is more positive than it was in the fourth quarter of last year.”

“ Low oil prices, a much weaker euro exchange rate, and the ECB’s introduction of a large and open-ended quantitative easing program are giving a boost to consumer demand and growth in the monetary union,” it added.

The agency, however, raised concerns that Greece’s future in the euro zone could still pose further risks to financial markets, and that the slowdown in key emerging markets could dent euro zone exports.

“We believe the member states’ varying levels of success in restoring their economic competitiveness through structural reforms will continue to play out in uneven performance,” it added.

Additional reporting by Reuters