The Federal Criminal Office said they were aware of a threat made by German Salafist Silvio K., who is believed to be fighting in Syria for ISIS.
But, the office, said there were "no indications of concrete attack plans or an impending attack".
Silvio has reportedly threatened to attack the Büchel facility near the western city of Koblenz, where US nuclear weapons are stored.
The Westdeutsche Allgemeine Zeitung (WAZ) reported on Thursday that security around the facility had been stepped up.
“We are working closely with the German authorities,” a spokesman for the US embassy in Berlin said.
An international arrest warrant was put out for Silvio in July.
Silvio was born in Saxony and lived in Essen and then Solingen in North Rhine-Westphalia. He is thought to be a member of the banned German Salafist group Millatu Ibrahim.
"He is a star of the Jihad scene and has between 5,000 to 10,000 Salafist supporters in Germany," terror export Guido Steinberg told WAZ.
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