Germany is on high alert after federal officials received intelligence information that Islamic militants already inside the country may be planning terror attacks against the nation.

“Security officials in Berlin said on condition of anonymity…that three scenarios existed—one involving senior al Qaeda leader Younis al Mauretani, another involving the Mumbai-style attack, and a third pointing to sleeper cells already in Germany,” Reuters reported.

Authorities are concerned that the latest threat—a suitcase containing batteries, a detonator and clock, discovered in Windhoek, Namibia, and bound for Munich—could be a precursor of other attacks on Germany. An American company confirmed that the detonator was a security test device that it had manufactured, but Namibian officials do not know who planted the suitcase.

“The discovery of the package — which German police said contained batteries along with the detonator and clock — caused jitters in Germany a day after German Interior Minister Thomas de Maiziere issued an unprecedentedly stark warning about possible militant attacks next week,” National Post reported.

In response to the threats, German police increased armed presence at possible target locations throughout the country, including airports, train stations and soon-to-open Christmas markets.

According to BBC News, “Germany may be a target because its troops are in Afghanistan, though not in a frontline role—its post-World War II constitution forbids that. But it also seems [a] likely target because of its central position in Europe.”