Security at the former embassy was tightened in the 1980s and 1990s following successive terrorist attacks on U.S. embassies and consulates worldwide . However , it was after the September 11 attacks in 2001 that security was significantly increased . A massive security operation at the embassy has seen one side of Grosvenor Square closed to public access by car , and armed roadblocks are stationed outside the building . On August 29 , 2002 , Kerim Chatty , a Swedish citizen of Tunisian descent , was arrested at Stockholm-Västerås Airport trying to board a Ryanair Flight 685 destined for London Stansted Airport with a loaded gun in his luggage . Anonymous intelligence sources cited in the media claimed that the man was planning to hijack the aircraft and crash it into the United States embassy in London , using the rooftop eagle to identify it from the air . Sweden 's Security Service , Säpo , denied the claims and called the reports " false information " . The man was subsequently cleared of all terrorism-related charges
September 11 attacks
September 11 attacks
Embassy of the United States, London