American and German officials fear a terrorist attack against U.S. military personnel or American tourists is imminent in Germany, ABC News reported Friday, but other officials said they have been on alert for some time.

"The information behind the threat is very real," ABC quoted a senior U.S. official as saying.

Click here to read the ABC report.

"The danger level is high. We are part of the global threat by Islamist terrorism," German Interior Minister Wolfgang Schauble told reporters.

But U.S. officials confirmed to FOX News that the threat is not new and dates back to an April 20 warning issued by the U.S. Embassy in Germany regarding unspecified threats to U.S. interests and/or Americans in that country.

A U.S. official told FOX News the threat is considered real, although not new, and is believed to involve one or more Middle Eastern Kurdish groups perhaps associated with Al Qaeda.

While this threat is being judged by both U.S. and German officials as serious, a U.S. official said much less is known about the specifics, including when and where such an attack might occur.

U.S. and German law enforcement officials told ABC that Patch Barracks, the headquarters for U.S. European Command, located near Stuttgart, is of particular concern.

But a U.S. military source told FOX News the threat conditions at Stuttgart are still at 'Bravo' and have not been raised.

"The press reports have added a sense of urgency that isn't there," the source said, adding there are no specifics to the threat beyond what was issued April 20.

"We have stepped up vigilance in Germany and in Western Europe at bases in Italy. We are flexing our force posture but threat conditions have not been raised," the source said. "There is not actual intelligence that gave U.S. and German officials a sense of an imminent threat, but we are maintaining vigilance at the base."

Since the investigation into the Sept. 11, 2001 attacks found the hijackers' planned their operation out of Hamburg, Germany, the country continues to be known as a staging area for Al Qaeda and groups affiliated with it.

Germany has been on a heightened state of alert for some time now because of threat information suggesting that a plot may exist and may very well be in the advance stages.

FOX News' Jennifer Griffin, Catherine Herridge and Nick Simeone contributed to this report.