BERLIN (AP) – American diplomatic buildings in Germany have increased their security in response to a “heightened threat” that they could be targeted, officials said Friday.

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

The American Embassy said “U.S. diplomatic and consular facilities in Germany are increasing their security posture.” The embassy refused to say if there was a specific threat, but urged Americans in Germany to “increase their vigilance and take appropriate steps to bolster their own personal security.”

“We are taking these steps in response to a heightened threat situation,” the embassy said.

In Washington, State Department spokesman Sean McCormack would not specify the nature of the threat but said the United States took it seriously enough review security at the Berlin embassy and U.S. missions in Bonn, Bremen, Dusseldorf, Frankfurt, Hamburg, Lepizig and Munich.

“It is serious enough and credible enough that we believed that we were obliged to put out the warden message warning Americans in Germany to be vigilant and exercise extra caution,” he told reporters.

Germany’s Interior Ministry said there were indications American buildings in the country could be targeted, but refused to give details.

German federal police in March said Germany faces an increased threat of terrorism because its military takes part in missions in Afghanistan and elsewhere.

Thousands of American servicemen and women are stationed with their families in Germany, which hosts key installations including Ramstein Air Base, Landstuhl Regional Medical Center and Grafenwoehr training center.

The American military in Germany has not changed its security arrangements for the moment, said Air Force Major John Dorrian, a spokesman for the American European Command in Stuttgart.