"At the summit today, Europe's heads of state and government must follow words with action: They should commit to adopting the EU Data Protection Reform by spring 2014. This would be Europe's declaration of independence. Only then can Europe credibly face the United States."
Even before the latest allegations, Germany and other nations had expressed concerns about alleged U.S. spying after Snowden -- a former National Security Agency contractor -- leaked classified information about American surveillance programs.
German news magazine Der Spiegel reported in June that leaks from Snowden detailed how the agency bugged EU offices in Washington and New York, and conducted an "electronic eavesdropping operation" that tapped into an EU building in Brussels.
Merkel spoke with Obama by phone in July about allegations that the United States was conducting surveillance on its European allies.
Merkel made it clear that if the information about the U.S. having monitored her phone were true, it would be "completely unacceptable," spokesman Steffen Seibert said of Wednesday's call with Obama.
A spokesman for David Cameron declined to answer questions Thursday about whether the British Prime Minister's phone had been tapped by the United States, following Germany's suspicion about U.S. monitoring of Merkel's cell phone.
"I am not going to comment on matters of security or intelligence," the spokesman told reporters at a regular briefing.
Ayrault: 'Shocking' claims
Ayrault described the report of widespread spying by the NSA on French calls as "worrying" and "shocking," saying that security should not be guaranteed at the price of a loss of freedom.
However, U.S. Director of National Intelligence James Clapper suggested that the claims made by Le Monde were false.
The articles "contain inaccurate and misleading information regarding U.S. foreign intelligence activities," a written statement from his office said Tuesday. It added that the United States does gather intelligence of "the type gathered by all nations."
Nonetheless, the allegations prompted a flurry of diplomatic activity this week between the United States and France.
Obama and French President Francois Hollande spoke about the claims Monday.
"The President and President Hollande discussed recent disclosures in the press -- some of which have distorted our activities and some of which raise legitimate questions for our friends and allies about how these capabilities are employed," a White House statement said.
"The President made clear that the United States has 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."
Hollande's office said the President expressed his "deep disapproval with regard to these practices" to Obama and that such alleged activities would be unacceptable between allies and friends.
The two Presidents agreed that French and American intelligence services would cooperate on investigating the report, according to the statement from the French President's office.
French Foreign Minister Laurent Fabius and U.S. Secretary of State John Kerry also met Tuesday to discuss the claims. The U.S. ambassador to France, Charles Rivkin, was summoned to the French Foreign Ministry in Paris on Monday to discuss the alleged spying.
Claims of U.S. spying, resulting from leaks by Snowden, have also soured U.S. relations with Mexico and Brazil.
Der Spiegel recently published allegations, citing Snowden as its source, that the U.S. National Security Agency "systematically" eavesdropped on the Mexican government and hacked the public e-mail account of former Mexican President Felipe Calderon.