Berlin , Germany ( CNN ) -- Germany has indefinitely closed off access to the general public to the cupola and the rooftop terrace of the Reichstag parliament building , the parliament 's press office said Monday . Accredited groups of visitors can still access the building , as can visitors to the restaurant on the roof . A cupola is a dome-like accent , normally located on the top of a building . The Reichstag cupola is multi-storied providing views of the Berlin landscape and also the main hall of parliament below . The German Bundestag is the only parliament building in the world to house a public restaurant , according to its operators . The press office said access to the building was limited due to security reasons , but did not elaborate . On Saturday , German police denied a news report that said terrorists may have been planning a strike on the parliament building , saying no specific attack threat exists . `` We have no firm lead on a specific location of a potential attack , or names or groups , '' said Joerg Ziercke , head of the Federal Criminal Police Office . Der Spiegel , a German weekly magazine , reported earlier Saturday that members and associates of al Qaeda were planning an attack on the building in Berlin . The building is a top tourist destination . The magazine did not identify its sources , which reportedly said the group would seek to take hostages . `` What Der Spiegel wrote is to be seen and understood in context with the overall assessment of potential targets being possibly highly symbolic places , buildings , venues , '' said Ziercke . `` We investigate some specific persons , but we can not yet make connections to specific threats on specific locations or type of attacks . Der Spiegel is speculating . '' The magazine reported that information about the planned attack came from a `` jihadist '' who wants to abandon the group . According to the tipster , the terror cell is made up of six people , two of whom are already believed to be in Berlin , Der Spiegel said . Earlier this week , Interior Minister Thomas de Maiziere said concrete evidence had emerged of a possible attack planned in Germany , but he did not offer specifics . The United States issued a general travel alert for Americans in Europe last month amid concerns that al Qaeda or related groups might be planning attacks similar to the 2008 massacre in the Indian city of Mumbai .
Der Spiegel reports an attack may have been planned on the Reichstag building . The publication does not identify its sources . - German Chancellor Angela Merkel says she is "shocked and saddened" by a shooting at Berlin's Christmas market that killed 12 people and injured 48.