Warning for Americans

A statement posted on the embassy's Web site urged "Americans in Germany to increase their vigilance and take appropriate steps to bolster their own personal security."

The statement did not refer to a specific threat, but a worldwide caution issued by the US State Department on April 10 warned that "al Qaeda and affiliated organizations continue to plan terrorist attacks against US interests in multiple regions, including Europe."

"The US government facilities constantly assess their security postures in light of information related to this heightened threat environment," said Robert Wood, a US spokesman at the US embassy in Berlin.

Without going into specifics of the type of danger posed, an embassy officials told Reuters that the warning was issued in connection with an increased threat of terrorism.

Iraqi group

Berlin's Tagesspiegel daily reported that an Iraqi militant group, Answar al-Sunna, was planning to carry out attacks on US installations and American citizens in Germany.

The newspaper quoted US intelligence sources as saying that supporters of the group had been seen observing US installations in southern Germany.

The group, based in northern and central Iraq, has been active in fighting the US-led occupation and the US-backed Iraqi government of Prime Minister Nuri al-Maliki.

Heightened vigilance

Though Germany has not been a target of international terrorism, officials, including the Interior Minister Wolfgang Schaüble, have urged vigilance after two unexploded suitcase bombs were discovered on regional trains in western Germany last summer.

Schäuble has also recently said that the threat of terrorism in the country has increased as it takes part in military missions in Afghanistan. In addition to some 3,000 Bundeswehr soldiers stationed mainly in northern Afghanistan, six Tornado reconnaissance warplanes were deployed to aid NATO-led troops in the country.

At a conference in March, Jörg Ziercke, head of the Germany's Federal Criminal Police Office, said the abstract danger of an attack in Germany had grown. He added that there was no reason for panic, as there were no solid indications of a pending attack.