According to the German news magazine Der Spiegel, Islamic extremists are planning an attack on the German parliament building, the Reichstag.
The reports suggest that al Qaeda and associated Islamist groups are planning to take hostages and fire at people in the building, which is both the seat of parliament and a popular tourist destination in Berlin.
The information reportedly comes from a jihadist who contacted the German authorities. Der Spiegel said the informant has repeatedly telephoned the German police from a foreign location in recent days, and is part of a terrorist cell of six people.
Two members of the cell are said to have been in Berlin for six to eight weeks and the attacks are reportedly planned for February or March 2011.
The magazine did not name its source.
Boosted security presence
Der Spiegel claims it is on the basis of this source's information that the Interior Minister Thomas de Maiziere warned earlier in the week that Islamists had planned attacks in Germany.
Security was increased at airports and train stations across Germany on Wednesday, when de Maiziere said there were "concrete" indications that militants were planning attacks.
He added there was "reason for concern, but not for hysteria."
Chancellor appeals for caution