Warning that Europe risks a "stagnation trap," leading French and German economists have proposed reforms and investments to revive growth in the eurozone's two biggest economies, but Berlin swiftly dismissed a key proposal to boost its public investment.

Henrik Enderlein, of Germany's Hertie School of Governance, and Jean Pisani-Ferry, head of the France Strategie government think tank, offered an implicit trade off between shaking up the rigid French labor market and regulated professions, and a public investment boost in creaking German infrastructure.

"The biggest danger we see right now is a period of window dressing where lip service is paid to grand projects and reforms, but no real steps are taken," they said, noting both countries face elections in 2017 and there was no time to lose.