An Interior Ministry spokesman said an "Islamist dimension" had been behind the decision announced on Friday, adding he would not "speculate" on various press reports.

According to Saturday's Der Tagesspiegel, an extremist Iraqi group, Ansar al Sunna, was planning attacks on US citizens and facilities in Germany.

Der Spiegel magazine reported that German authorities had been warned by the CIA that an Islamist Kurdish group was thought to be planning an attack in Germany or a neighboring country.

"Heightened threat"

The US embassy in Germany said Friday it was increasing security at US facilities in the country in response to "a heightened threat situation", although Washington played down the danger.

The State Department in Washington stressed that the embassy alert was not sparked by any "specific or credible" information about threats directed against US interests in Germany.

Spokesman Tom Casey said the alert was based on "generic, unspecific information."