A return to expansion in France and Italy helped boost eurozone economic growth in the first three months of 2015 to its fastest pace in almost two years, broadening a modest revival that had previously been heavily reliant on Germany.

For the first time since the first half of 2010, all four of the eurozone's largest economies recorded growth. And for the first time since the first quarter of 2011, the currency area's economy grew more rapidly than both the U.S. and the U.K.

That combination of faster and more evenly spread growth will feed hopes that 2015 could mark a decisive year for the eurozone in its efforts to recover from its debt crisis, aided by fresh stimulus from the European Central Bank, a weakening euro, lower oil prices and signs that bank lending may be set to increase after years of decline.

However, policy makers have openly expressed worries that the recovery may not be sustained, citing high unemployment, high government and corporate debt burdens, banking-system problems and weak investment spending. They contend that politically difficult overhauls in France and Italy, and an increase in investment in crumbling infrastructure in Germany and elsewhere, are the only way to achieve lasting growth in Europe.

The combined gross domestic product of the 19 countries that shared the euro was 0.4% higher in the first quarter than in the final three months of 2014, the European Union's statistics agency said Wednesday. That marked a pickup from the 0.3% growth recorded in the final quarter of last year, but was slightly weaker outcome than the 0.5% rate forecast by many economists.

On an annualized basis, the economy grew 1.6%.

Germany's economy, the eurozone's largest, slowed more sharply than expected, to record growth of 0.3% compared with 0.7% in the previous period. But France and Italy both exceed expectations, growing 0.6% and 0.3% respectively, having stagnated in the previous period.

French Finance Minister Michel Sapin struck an unusually confident tone Wednesday, saying he expected the French economy to grow at least 1% this year and 1.5% in 2016.

However, he warned the first quarter was unlikely to reverse France's persistent double-digit jobless rate, and that the government must press ahead with politically difficult reforms.

"We must not only take note of good news, we need to keep it up," Mr. Sapin told BFM TV.

Figures released earlier from Spain showed its economy led the recovery with a 0.9% growth rate.

The currency area's long slump has taken a toll on confidence. Businesses have grown accustomed to weak growth and are wary of investing as a result, while unemployment remains near record highs, making households reluctant to spend.

The confrontation between Greece's new, leftist government and its German counterpart over the terms of its bailout is a more imminent threat to the currency area's revival. Although it has had little negative impact on other parts of the eurozone to date, a debt default by the Greek government, possibly followed by the nation's departure from the eurozone, would likely be very damaging to currency area as a whole.

Write to Paul Hannon at paul.hannon@wsj.com and Stacy Meichtry at stacy.meichtry@wsj.com