The U.S. authorities have discovered a terrorist plot in the advance stages of planning against U.S. facilities in Germany, CNN reported Friday.

The official said the plot, which has been planned for some time, included the use of bombs and small arms against U.S. targets -- possibly military facilities, buildings or U.S. citizens.

He called it a "very real threat" and said an al-Qaida affiliate franchise in Europe might be responsible for the plot.

However, a senior Pentagon official said there is "nothing new" beyond what led the U.S. State Department to issue a warden message raising security at American facilities three weeks ago.

A spokesman for the U.S. Embassy in Berlin and a spokesman for the German Interior Ministry also said they're not aware of a new threat beyond what led to that message.

Meanwhile, the Department of Homeland Security issued a statement saying there was no credible intelligence to suggest an imminent threat on U.S. soil.

In a related development, U.S. air marshals are providing additional protection of flights between Germany and the United States, law enforcement officials.

Germany, which will host the G-8 Summit next month, has been engaged in a security crackdown recently.

More than 900 personnel took part in anti-terror raids, arresting more than 40 people.