It is not clear if the video, which has a soundtrack of machine-gun bursts and exploding shells, comes from Islamists. The images include a text saying Berlin, Cologne and Bremen will be attacked.

The ministry said YouTube took down the video on January 12. The US website deletes offensive material as soon as users spot it.

German security authorities were analysing a copy of the video. Focus, a German news weekly, said the religious expressions that are usual in Islamist threats were conspicuously absent from the anonymous video.

"We are going to send an army into the middle of your cities, especially Berlin, Cologne and Bremen," the text in the video said, according to Focus. "Germany and four other nations will be in trouble from February '09."

A week ago, Germany was threatened in an Islamist video that indicated sympathies with al-Qaeda.