The European Bank for Reconstruction and Development Thursday urged the European Central Bank to launch a large-scale program of asset purchases known as quantitative easing, becoming the latest international organization to signal that the package of stimulus measures announced earlier this month won't solve the eurozone's twin problems of low growth and inflation.

On Sept. 4, ECB President Mario Draghi announced new cuts to its key interest rates along with programs to buy asset-backed securities and covered bonds, having...