PARIS—French President François Hollande said Monday the European Central Bank will decide to buy government debt later this week, reinforcing expectations the Frankfurt-based institution will follow other major central banks into so-called quantitative easing.

“On Thursday, the ECB will take the decision to buy sovereign debt, which will provide significant liquidity to the European economy and create a movement that is favorable to growth,” Mr. Hollande said in a speech to business leaders at the Élysée Palace.

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