(CNN) -- German Chancellor Angela Merkel said Thursday that trust between Europe and the United States must be "re-established" after claims the U.S. National Security Agency eavesdropped on her cell phone.
Merkel commented as she arrived at a summit of European Union leaders in Brussels, Belgium. The summit risks being overshadowed by anger about allegations the United States has been spying on its allies.
"We need trust, and now the trust has to be re-established," she said. "Spying among friends is never acceptable.
"Now we have to discuss what sort of data protection do we need and what sort transparency is there."
Merkel discussed the issue with U.S. President Barack Obama on Wednesday, after the German government said it had information that the United States might have monitored her cell phone.
She told Obama that eavesdropping among friends is "never acceptable, no matter in what situation," she said.
On Thursday, when asked to clarify whether the United States has monitored Merkel's cell phone, White House spokesman Jay Carney said the White House does not comment on every alleged intelligence activity. He said again what he said Wednesday -- that Obama assured Merkel that the United States is not monitoring and will not monitor her communications.
"When it comes to specific allegations about intelligence matters, we have diplomatic ... channels we use in order to discuss these issues," Carney told reporters.
The U.S. ambassador to Germany, John B. Emerson, was summoned to a meeting with German Foreign Minister Guido Westerwelle on Thursday, the German Foreign Ministry said. Germany will make its position clear at that meeting, a spokeswoman said.
The German allegation comes in the same week that French daily newspaper Le Monde reported claims that the U.S. National Security Agency intercepted more than 70 million phone calls in France over 30 days.
And The Guardian newspaper -- citing a document from U.S. government contractor-turned-whistleblower Edward Snowden -- reported Thursday that the National Security Agency had monitored phone conversations of 35 world leaders. The confidential memo is from 2006, which is before Obama became president. None of the monitored world leaders is identified.
The phone numbers were among 200 handed over to the NSA by a U.S. official, the memo states. Others were encouraged to share their "rolodexes" with the agency, according to the document, even though tracking until then had yielded "little reportable intelligence."
Like Carney, NSA spokeswoman Caitlin Haden refused "to comment publicly on every specific intelligence activity."
"As we have made clear," she added, "... the United States gathers foreign intelligence of the type gathered by all nations."
European leaders push for data protection
It's not clear how well such explanations will be received by Washington's allies in Europe elsewhere, or how significantly it will affect the European Council meeting.
The two-day meeting was supposed to focus on the digital economy and economic and social policy issues, as well as concerns about EU migration, after a recent shipwreck off an Italian island in which hundreds of migrants from Africa died.
But French Prime Minister Jean-Marc Ayrault told the French National Assembly on Tuesday that France would ask for the question of electronic surveillance to be added to the agenda.
The EU leaders were expected to discuss data protection issues as part of their debate on the digital economy.
Viviane Reding, vice president of the European Commission, called for EU nations to commit to adopting a data protection law in light of the recent spying scandals.
"Data protection must apply to everyone -- whether we are talking about citizens' e-mails or Angela Merkel's mobile phone," she said. "We now need big European rules to counter big fears of surveillance.
"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.