BERLIN — Leaders and citizens in Germany, one of America’s closest allies, simmered with barely contained fury on Thursday over reports that American intelligence had tapped into Chancellor Angela Merkel’s cellphone, the latest diplomatic fallout from the documents harvested by the former National Security Agency contractor Edward J. Snowden.
In an unusual move between staunch allies, Germany summoned the United States ambassador over the claims.
Ms. Merkel herself angrily demanded assurances from President Obama that her cellphone was not the target of an American intelligence tap as soon as suspicions surfaced on Wednesday. Washington hastily pledged that her calls were not being monitored and would not be in future but conspicuously said nothing about the past.
While the chancellor kept quiet before heading to Brussels for a European summit on Thursday, one of her closest allies, Defense Minister Thomas de Maizière, gave full voice to the shock expressed by politicians and citizens.
“If that is true, what we hear, then that would be really bad,” Mr. de Maizière told ARD, Germany’s leading state television channel. America is Germany’s best friend, he noted, adding: “It really can’t work like this.”
He suggested that there would be consequences. “We can’t simply go back to business as usual,” he said.
Katrin Göring-Eckardt, the leader of the Greens, shared the indignation, noting that America is a close ally but that normal business could not be conducted “if we go about suspecting one another.”
Her consternation was mixed with an element of “we told you so.” The Greens had argued since the first disclosures last summer of mass American surveillance that Ms. Merkel needed to be more vigorous and not simply accept American assurances that no German laws had been broken.
That was also a strong strand in online comments pouring into German media Web sites.
Ms. Merkel’s angry call to Mr. Obama was the second time in 48 hours – after a similar furor in France prompted Mr. Obama to call President François Hollande — that the president found himself on the phone with a close European ally to argue that continuing revelations of invasive intelligence gathering should not undermine decades of hard-won trans-Atlantic trust.
Both episodes illustrated the diplomatic challenge to the United States posed by the cache of documents that Mr. Snowden handed to the journalist Glenn Greenwald and others. Last week, Mr. Greenwald concluded a deal with the eBay founder Pierre Omidyar to build a new media platform that aims in part to publicize other revelations from the data Mr. Greenwald now possesses.
The damage to core American relationships continues to mount. Last month, President Dilma Rousseff of Brazil postponed a state visit to the United States after Brazilian news media reports — fed by material from Mr. Greenwald — that the N.S.A. had intercepted messages from Ms. Rousseff, her aides and the state oil company, Petrobras. Recently, the German newsmagazine Der Spiegel, which has said it has a stack of Snowden documents, suggested that United States intelligence had gained access to communications to and from President Felipe Calderón of Mexico while he was still in office.
Secretary of State John Kerry had barely landed in France on Monday when the newspaper Le Monde disclosed what it said was the mass surveillance of French citizens, as well as spying on French diplomats. Furious, the French summoned the United States ambassador, Charles H. Rivkin, and Mr. Hollande expressed “extreme reprobation” for the reported collection of 70 million digital communications from Dec. 10, 2012, to Jan. 8, 2013.
In a statement published online, James R. Clapper Jr., the director of national intelligence, disputed some aspects of Le Monde’s reporting, calling it misleading and inaccurate in unspecified ways.
He did not address another report by Le Monde that monitoring by the United States had extended to “French diplomatic interests” at the United Nations and in Washington. Information garnered by the N.S.A. played a significant part in a United Nations vote on June 9, 2010, in favor of sanctions against Iran, Le Monde said.
Two senior administration officials — from the State Department and the National Security Council — had arrived in Berlin only hours before the German government disclosed on Wednesday that it had received unspecified information that Ms. Merkel’s cellphone was under surveillance.
If confirmed, that is “completely unacceptable,” said her spokesman, Steffen Seibert. The accusations followed Der Spiegel’s disclosures in June of widespread American surveillance of German communications, which struck an especially unsettling chord in a country scarred by the surveillance undertaken by Nazi and Communist governments in its past.
Mr. Seibert quoted the chancellor, who was raised in Communist East Germany, as telling Mr. Obama that “between close friends and partners, which the Federal Republic of Germany and the United States of America have been for decades, there should be no such surveillance of the communications of a head of government.”
“That would be a grave breach of trust,” Mr. Seibert quoted her as saying. “Such practices must cease immediately.”
The government statement did not disclose the source or nature of its suspicions. But Der Spiegel said on its Web site that Ms. Merkel acted after it submitted a reporting inquiry to the government. “Apparently, after an examination by the Federal Intelligence Service and the Federal Office for Security in Information Technology, the government found sufficient plausible grounds to confront the U.S. government,” Der Spiegel wrote.
ARD, Germany’s premier state television channel, said without naming its sources that the supposed monitoring had targeted Ms. Merkel’s official cellphone, not her private one.
About an hour after the news broke in Berlin, Jay Carney, the White House spokesman, appeared before news media in Washington, reporting the Obama-Merkel phone call and saying that “the president assured the chancellor that the United States is not monitoring, and will not monitor, the communications of the chancellor.”
Mr. Obama pledged, as he had to Mr. Hollande, and to Mexico and Brazil, that intelligence operations were under scrutiny and that he was aware of the need to balance security against privacy.
The first disclosures from Der Spiegel in June almost soured the long-planned meeting between Mr. Obama and Ms. Merkel in her capital, which the president visited as a candidate in 2008, delivering a speech before an estimated 200,000 people.
In June, there were far fewer, carefully screened and invited Germans and Americans on hand to hear Mr. Obama at the Brandenburg Gate, the symbol of Berlin’s unity and freedom since the Berlin Wall fell in 1989.
Shortly beforehand, Mr. Obama and Ms. Merkel stood side by side in her chancellery, fielding questions about American surveillance of foreigners’ phone and e-mail traffic. Pressed personally by Ms. Merkel, the president said that terrorist threats in Germany were among those foiled by intelligence operations around the world, and Ms. Merkel concurred.
Senior intelligence officials have since made plain that cooperation between the United States and Germany in the field is essential to tracking what they view as potential terrorist threats.
But if indeed American intelligence was listening to Ms. Merkel’s phone, or registering calls made and received, the trust between Berlin and Washington could be severely damaged. Since June, even senior officials in the German government have voiced more caution about cooperating with the United States and wondered in private about the extent to which any information gleaned was shared with, for example, business rivals of German companies.
The German government said it had been assured that German laws were not broken, but the issue remains politically fragile.
In July, Ms. Merkel joked with television interviewers who asked about the situation, “I know of no case where I was listened to.”
At a separate news conference that month, she signaled on a more serious note that she understood the importance, for all Western allies, of collecting intelligence. But she also emphasized that German or European laws should not be violated.
The alarm of Americans — and, indeed, their allies — after the attacks of Sept. 11, 2001, was understandable, Ms. Merkel said then, but “the aim does not justify the means. Not everything which is technically doable should be done. The question of relative means must always be answered: What relation is there between the danger and the means we choose, also and especially with regard to preserving the basic rights contained in our Basic Law?”