Rich nations will turn in unexpectedly strong growth in the first half of 2012 but leading European economies will lag behind the United States, the OECD said on Thursday.

Raising its estimate for growth of the US economy by about two thirds from 1.7 to 2.8 percent, the Organisation for Economic Cooperation and Development gave a broadly upbeat view of the recovery from the financial crisis and the European debt crisis.

But this improved outlook is fragile, notably because of the easing but still unresolved debt strains in the eurozone and owing to the rise in the price of oil, the organisation said.

Central banks in most of these leading economies should pursue their easy money policies for some time, the OECD advised.

"Growth is expected to be firmer through the first half of the year," the OECD said in a report focused on the economic outlook in the rich G7 nations.

"Short-term prospects have improved relative to the situation prevailing in late 2011, but indicators still suggest a fragile recovery," the OECD said.

The new forecast for the first half of 2012 pointed to a "decoupling" between the United States and Canada which should see "robust growth", and Europe where "the outlook remains weak", the organisation said.

As the United States expanded, the OECD said first half growth would diverge in Europe with Germany rebounding and France, Italy and Britain contracting in the first quarter.

The United States should see growth in the first quarter of 2012 reach 2.9 percent on a 12-month basis, up from an earlier forecast of 1.7 percent, and grow 2.8 percent in the second quarter, up from 1.9 percent.

The US Commerce Department said Thursday the US economy grew at an annual rate of 3.0 percent in the fourth quarter of last year, and by 1.7 percent for all of 2011.

Growth prospects within the eurozone, stuck in the throes of a debt crisis since 2010, will diverge as well, the OECD indicated.

"Recent positive indicators suggest that activity in Germany may accelerate through the first half of the year," the report said.

First-quarter growth in Germany will be 0.1 percent, firmer than an earlier forecast of a 0.3-percent contraction, and in the second quarter gross domestic product will expand by 1.5-percent, nearly twice the previously forecast figure of 0.8 percent.

Activity in France will be "broadly flat", the OECD said, with a contraction of 0.2 percent in the first quarter of 2012 and a recovery of 0.9 percent growth in the second quarter.

In Italy meanwhile "weak industrial production and household sentiment are suggestive of recession for the first two quarters of the year," the OECD said.

Britain, the only non-eurozone European nation in the G7, will contract by 0.4 percent in the first quarter of 2012 and recover to 0.5 percent growth in the second quarter.

For Japan the OECD projected a strong first-quarter rebound of 3.4 percent as the country recovers from the 2011 tsunami and a strong yen, but second quarter growth is projected to be a more moderate 1.4 percent.

The OECD stressed that oil prices posed a threat to the recovery in the G7 nations and to growth in all 34 of its member nations.

"The recent oil price increase will likely add around a quarter of a percentage point to inflation in the OECD economies and take off between 0.1 and 0.2 per cent from average OECD GDP over the next year," the report said.

With stockpiles high, France, Britain and the US are expected to turn to the OECD's International Energy Agency for a decision in favour of releasing oil from strategic stocks to help bring down prices.

The OECD said policy decisions took a key role in determining the better outlook, particularly in such a fragile context.

An expansionary monetary policy, with interest rates in most large OECD countries at very low levels, "will be warranted for a considerable time to come, as will maintaining support through quantitative measures," the report said.

On Tuesday, the OECD pressed the eurozone to implement a safety net of at least 1.0 trillion euros ($1.33 trillion) in order to ease market tensions and withstand possible future requests for financial rescue.

"We are not out of the woods," OECD Secretary General Angel Gurria had said, referring to the eurozone debt crisis that has festered for more than two years.