If the relationship between the Obama Administration and German Chancellor Angela Merkel weren’t frosty enough over the NSA spying on her phone — things got a lot more tense over the weekend.

With mystery enveloping a German intelligence service employee accused of spying — reportedly for the United States — German officials and commentators on Sunday angrily demanded a response from Washington, warning that an already troubled relationship was at risk of deteriorating to a new low.

The demands for a statement from the United States were nevertheless couched in cautious terms, suggesting that the scandal, which exploded on Friday when Germany’s federal prosecutor reported the arrest of the 31-year-old employee of the Federal Intelligence Service, might not be as bad as initially feared. The chairman of a parliamentary inquiry into American intelligence activities told German radio that it seemed there was no breach of security surrounding his committee’s work, as some news reports had suggested.

The revelations of a German spy acting as double agent for the United States is another piece of Edward Snowden’s information he stole from the National Security Agency when he was a contractor there. Release of classified information from Snowden last summer caused serious strains in the U.S.-German friendship.

Over decades of friendship since 1945, sharp language like that of recent months has been rare in German-American dealings. Those ties have been strained since last summer, when documents leaked by Edward J. Snowden, a former National Security Agency contractor, suggested that the N.S.A. had monitored the electronic data of millions of Germans.

The German government then appeared to receive assurances from Washington that nothing illegal had occurred. But the subsequent revelation that Ms. Merkel’s own cellphone had been monitored stirred new anger in a nation that remembers the role played by a snooping state under the Nazis and the Communists.

The news of the German double-agent come on the heels of a Washington Post expose using much of the data given to them by Snowden. Yesterday, the WaPo bombshell study of the documents revealed that most of the individuals caught up in the NSA data collection are innocent Americans — not foreign terrorist targets.