TRADE DEAL
Experts said that talks on a free trade deal between the European Union and United States, called the Transatlantic Trade and Investment Partnership (TTIP), may be affected; Berlin may push harder on some aspects of the deal in areas such as data protection - long a major concern for Germans after the abuses of the Nazi Gestapo and East German Stasi secret police.
"But the idea that Merkel would somehow try to torpedo TTIP is not really likely," said Germany expert Hans Kundnani at European Council on Foreign Relations in London.
John Kornblum, a former US ambassador to Germany who still lives in Berlin, said: "I believe the Germans are telling the Americans, 'We want to continue close cooperation but you've pushed us too far and have forced us to react'."
Merkel's government poured scorn on the alleged espionage.
Interior Minister de Maiziere said the information the United States appeared to have obtained was "laughable", contrasting that with the "disproportionate and serious political damage" the scandal had caused.
Merkel was "not amused", Finance Minister Wolfgang Schaeuble said, adding: "This is so stupid, it can only make you weep."
Tensions have risen since revelations last year stemming from documents leaked by Edward Snowden, a contractor with the US National Security Agency (NSA). Those caused Berlin to demand a mutual "no-spy deal" which Washington has resisted.
"Ever since the NSA disclosures broke last year, the issue of US spying has been an extremely sensitive issue in Germany," said Karen Donfried, president of the German Marshall Fund of the United States, which promotes US-European ties.
Some Americans asked whether the espionage activities were worth the bother: "I am not troubled that the United States conducts espionage, even against friendly states," said one former senior US intelligence official.
"I am troubled when we attempt espionage and do not do it well. We learn nothing and we embarrass a friend and ourselves."