Tourists are being turned away from The Reichstag in Berlin after reports of a plot to attack the German parliament building.

Three million people visit the cupola each year but only groups with an advance booking were allowed through police barricades.

The security measure has been brought in after a magazine reported armed Islamist extremists were planning to enter the 19th Century building and open fire.

The information police were basing their decision on is being called 'credible.'

Security at airports and train stations has already been tightened.

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.