In March 1968, a crowd of some 10,000 demonstrated at Trafalgar Square against US involvement in the Vietnam War, before marching to Grosvenor Square. The Metropolitan Police had attempted to cordon off part of the square nearest to the embassy and there was violence as the crowd broke through the police line. Police horses were used to regain control. 200 demonstrators were arrested and 50 people needed hospital treatment including 25 police officers, one of them with a serious spinal injury. In October of the same year, during a demonstration organised by the Vietnam Solidarity Campaign, a splinter group of 6,000 demonstrators returned to the square. A thousand police officers formed a cordon that the protesters failed to breach and remained relatively peaceful until the crowd began to disperse when there was disorder in the neighbouring streets. Security concerns 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 29 August 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. The security threat against the embassy prompted the U.S. government to consider moving the embassy. Several British media outlets reported that the U.S. government had wished to use Kensington Palace as their embassy, which allegedly had been vetoed by Queen Elizabeth II, as several members of the British Royal Family have their residences there. The embassy "strenuously denied" the reports, and a spokesman for Buckingham Palace reported that no formal request had been made. Another possible option was Chelsea Barracks, for which the U.S. Embassy made an unsuccessful bid in February 2007. New building On 8 October 2008, the embassy announced