Hollande's office said in a statement that he had expressed "deep disapproval of these practices, which are unacceptable between friends and allies because they infringe on the privacy of French citizens."

Hollande "asked that all explanations be provided, as well as all information that could be at the disposal of former NSA consultant Edward Snowden."

The statement said the two leaders had agreed "to work together to determine the facts and the exact scope of surveillance activities" revealed by French newspaper Le Monde.

The two stressed that surveillance operations should be put into a "bilateral framework" and agreed that US and French intelligence agencies would "work together to this effect," the statement said.

NSA secretly recorded millions of phone calls made in France, French daily "Le Monde" reported on Monday, citing documents leaked by former NSA intelligence contractor Edward Snowden, who has taken temporary refuge in Russia.

The allegations risked turning into a diplomatic row just as US Secretary of State John Kerry arrived in Paris for the start of a European tour over Syria.

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