Officials in Germany have cautioned authorities to prepare for possible attacks against United States facilities overseas as revelations continue to emerge about America’s secretive National Security Agency.

As leaked classified documents continue to disclose the covert operations of the NSA, a domestic intelligence warning obtained by Germany’s Der Spiegel suggests the revelations made possible by former contractor Edward Snowden’s leaked files are inspiring potentially violent protests.

Der Spiegel, an outlet which has worked closely with Snowden and some of the leaked documents since earlier this year, announced on Monday that it had received a domestic intelligence memo from Germany's Federal Office for the Protection of the Constitution - the contents of which cautioned officials that "an emotional response from certain segments of the population cannot be ruled out.”

According to the magazine, the government office said that a “potential threat” had emerged following the information disclosed by the NSA leaks, adding that "security measures aimed at protecting US facilities in Germany should be increased."

Anti-American sentiment has spread across the globe in recent weeks as Snowden’s leaks continue to expose evidence of questionable surveillance operations conducted by the NSA - including recent revelations in which the agency was linked to violating the privacy of German citizens and even the country’s chancellor, Angela Merkel.

A poll published in the wake of those revelations by public broadcaster ARD suggested that only 35 percent of German citizens still see the US as a reliable partner. At the dawn of US President Barack Obama’s first term as president, more than three-quarters of Germans polled in a similar survey said they trusted America.

Earlier this week, Sen. John McCain (R-Arizona) called for the head of the NSA to leave office. Snowden’s leaks have caused much embarrassment in Washington since June, and former friends of the US have demanded answers after being told through leaked documents that they’ve been subjected to surveillance.

“The head of the NSA, the president of the United States, the Congressional Intelligence Committees [and] all of these contractors we pay that were responsible for performing the background checks” should be considered for “wholesale housecleaning,” McCain told Der Spiegel in an interview published over the weekend.

“Friends spy on friends. We all know that, but there have been certain boundaries,” added McCain. “Those boundaries were probably, to some degree, there because we didn't have the capabilities we have now. But when you go to the point where you invade someone's privacy...one of the most foremost leaders in the world, Angela Merkel, then it was a mistake.”

According to Der Spiegel, the head of Germany’s Office for the Protection of the Constitution demanded “urgent clarification” with regards to the heightened security alert, but had not received a reply from federal authorities as of Tuesday.