WASHINGTON (AFP) - The White House on Monday brushed off France's complaints about new allegations of eavesdropping by a top United States espionage agency, saying "all nations" conduct spying operations.

French Prime Minister Jean-Marc Ayrault earlier said he was "deeply shocked" by reports that the US National Security Agency had secretly monitored tens of millions of phone conversations within France, and demanded an explanation.

The White House, in line with its normal procedure, declined to comment on the specific charges, which outraged its ally.

"As a matter of policy, we have made clear that the United States gathers foreign intelligence of the type gathered by all nations," said National Security Council spokesman Caitlin Hayden.

"As the President said in his speech at the UN General Assembly, we've begun to review the way that we gather intelligence, so that we properly balance the legitimate security concerns of our citizens and allies with the privacy concerns that all people share."

Mr Ayrault said during a trip to Denmark that it was "incredible that an allied country like the United States at this point goes as far as spying on private communications that have no strategic justification, no justification on the basis of national defence".

US Ambassador to France Charles Rivkin was summoned to the Foreign Ministry in Paris over the claims, based on leaks from fugitive US former security analyst Edward Snowden and published by Le Monde and the German weekly Der Spiegel.