German Interior Minister Hans-Peter Friedrich speaks after the session of the Parliamentary Control Committee on the U.S. National Security Agency spying scandal (Britta Pedersen/European Pressphoto Agency)

German Chancellor Angela Merkel grew up in a society where the government kept a Big Brother eye on its citizens. Now, critics say, she has assented to similar practices — this time coming from the United States, not East Germany’s fearsome secret police.

Revelations about U.S. surveillance around the world shocked many Europeans when details were leaked by Edward Snowden, a former contractor with the National Security Agency. Now critics are questioning their own leaders about whether they were complicit in monitoring a wide swath of Internet and phone traffic, and nowhere has the anger been fiercer than in Germany, where citizens guard their personal information far more jealously than do their American peers.

With Merkel campaigning to win a third term in September elections, the American surveillance and allegations of German complicity have rapidly emerged as a central campaign issue, and the German leader has gone on a media blitz in recent days to assure voters that she was fighting for their rights. On Tuesday, she hardened her rhetoric, raising the possibility of prosecuting anyone who has broken German privacy laws.

“I want to say to our American partners that on German soil, German law always applies, and we will enforce it,” Merkel said Tuesday in a speech at an industry convention in Cologne. Earlier, referring to the Ministry of State Security, the secret police agency — better known as the Stasi — under the former German Democratic Republic, she had said that “there is absolutely no comparison between the Stasi of the GDR and the work of intelligence agencies in democratic states.”

Merkel has denied having specific knowledge of U.S. activity, saying that responsibility for the day-to-day chore of monitoring intelligence reports belongs to a subordinate in the chancellor’s office.

But critics — especially those in the opposition Social Democratic and Green parties — say that Merkel knows more than she is saying or has been willfully ignorant of collusion between German intelligence agencies and their American counterparts.

“If they don't know what happened, they must not want to know what has happened,” said Hans-Christian Ströbele, a member of the Green Party and the parliamentary committee that oversees Germany’s intelligence service. In reality, he said, the committee is able to do little oversight. “Our sovereignty ends at the door of the U.S. facilities in Germany,” he said.

On Wednesday, the question of German collaboration with U.S. surveillance was further complicated when the Bild newspaper published portions of a confidential September 2011 NATO document that discussed a PRISM program for online surveillance in Afghanistan to which German military commanders would have contributed nominations for people to be monitored by U.S. personnel.

Merkel’s spokesman acknowledged on Wednesday the existence of the NATO surveillance program in Afghanistan, but he said it was not identical to the one run directly by the United States.

French and British intelligence agencies are also alleged to have engaged in widespread surveillance activity.

The revelations about U.S. surveillance have become an issue in U.S.-European talks to remove trade barriers between the two economic blocs, negotiations that started this month. European lawmakers have demanded that talks with the United States about privacy and data protection be pursued in parallel with the trade discussions. French President François Hollande initially called for the trade talks to be put on hold — though that was before the newspaper Le Monde published a report alleging that French intelligence services were sweeping up nearly every piece of data that passes through French borders.

Germans have organized protests at one alleged NSA outpost outside Frankfurt. (The main organizer told the Spiegel newsmagazine that German police officers showed up on his doorstep after he wrote, jokingly, on Facebook about planning a nature walk around the U.S. facility.) In Berlin, one person projected a sign that said “United Stasi of America” on the wall of the U.S. Embassy.

And a top Merkel ally, Interior Minister Hans-Peter Friedrich, jetted to Washington last week to meet with Attorney General Eric H. Holder Jr. and Vice President Biden about the surveillance. On Tuesday, Friedrich briefed a parliamentary oversight committee about the outcome of the emergency visit, telling reporters after the closed-door meeting that if “technical possibilities for spying exist, they will be used,” and cautioning Germans to keep better watch over their data.

Opposition politicians called Friedrich’s trip an embarrassing failure, saying he had not pushed the U.S. government and had not learned anything new about apparently extensive U.S. monitoring of German nationals.

Despite the controversy over the spying revelations, German polls still rank Merkel as the most popular politician in the country by far, and analysts say it is still unclear whether she will be damaged by the tumult. A Forsa poll last week showed that 80 percent of Germans do not believe their government’s assurances that it was unaware of U.S. activity in Germany.

Although President Obama remains widely popular in Germany, his image has also taken a hit. Many Europeans were already concerned after revelations about terrorism-related surveillance, but subsequent disclosures in Britain’s Guardian newspaper and Der Spiegel that the United States had also spied on European diplomats led some holdouts to unload against the NSA.

“There’s a real element of surprise there and a disenchantment with the United States that this was happening,” said Johannes Thimm, an expert on U.S.-Europe relations at the German Institute for International and Security Affairs. “This has been a sobering moment in the sense that even Obama is an American president and someone who represents U.S. interests that might be fundamentally different from German interests.”

Now, some Germans are calling for a criminal inquiry aimed at anyone complicit in the U.S. surveillance efforts.

“Espionage of German institutions can be punished with up to 10 years of prison. The Federal Prosecutor’s Office should launch a criminal case,” said Wolfgang Neskovic, a former judge in one of Germany’s highest courts and now an unaligned member of Parliament. “Germany is a sovereign state, and it has to be made clear to the Americans that they cannot spy just because they are capable of doing it.”

Petra Krischok contributed to this report.