Germany's decision to step up security measures this week was prompted by discovery of militant plans to break into the Reichstag parliament building and shoot hostages, a German magazine said on Saturday.

The weekly Der Spiegel, citing security officials, said a jihadist living abroad had informed them in recent telephone calls of a plan for armed militants to enter the 19th century  building in central Berlin and open fire. It said police considered the information credible.

Germany's Federal Crime Office (BKA) had no immediate comment on the report.

The information, the magazine said, had prompted officials to announce on Wednesday they were raising security, especially at public places including airports and train stations.

Interior Minister Thomas de Maiziere said on Thursday authorities were on guard against threats of an armed attack of the kind that killed 166 in the Indian city of Mumbai in 2008.

The parliament building has strong symbolic importance in Germany. An arson attack there in 1933 highlighted Nazi moves to assume complete control in Germany. The image of a Soviet soldier planting the red flag atop its ruin in 1945 marked the end of World War Two for many.

It was formally restored as the country's legislature soon after the 1990 reunification of Germany and is visited daily by hundreds who walk around its glass dome looking down on debates.

The jihadist, Der Spiegel reported, said the group of attackers was to be made up of six people. Two had already arrived in Berlin and another four, including a German, a Turk and a North African, were under way.

Germany maintains a contingent of forces in Afghanistan and has been the target of threats on Jihadist websites.-Reuters