Berlin ? U.S. diplomatic buildings in Germany have increased their security in response to a “heightened threat,” and the U.S. Embassy warned Americans in the country to take precautions, officials said Friday.

German officials also said they have stepped up security outside U.S. bases, but left any specific danger unclear.

“U.S. diplomatic and consular facilities in Germany are increasing their security posture,” an embassy e-mail announcement read. The message encouraged “Americans in Germany to increase their vigilance and take appropriate steps to bolster their own security.”

Interior Minister Wolfgang Schaeuble said German police have stepped up protective measures outside American bases, though a U.S. air force official said the military had not taken any additional measures of its own.