Kenya attack: Sixth Briton dead in Westgate mall siege 28 September 2013 Last updated at 16:50 A sixth Briton has died following the siege at a shopping mall in the Kenyan capital Nairobi, the Foreign Office has confirmed. At least 72 people are known to have been killed in the four-day attack at the Westgate centre. The Foreign Office has said that it cannot rule out the possibility of further casualties. A Foreign Office spokesman said: "Our thoughts are with the family at this difficult time." The confirmed death toll after the three-day siege is 61 civilians, six security officers and five militants. Kenya's Red Cross says 61 people are still missing. Forensic experts, including a team from the UK, have been combing the complex, looking for bodies and clues, since the siege - which began last Saturday - ended on Tuesday. Official mourning The role of the British forensic scientists, sent by the Metropolitan police, has been to support the British High Commissioner in Nairobi identifying British victims and to advise Kenyan authorities. Kenya has observed three days of official mourning for victims after officials urged the nation to come together in the wake of the attacks. Eleven people have been arrested in connection with the siege, which al-Shabab, an Islamist group based in neighbouring Somalia, is claiming responsibility for. None of the dead Britons has been formally identified, but they are believed to include Ross Langdon, who had dual Australian and British nationality, and eight-year-old Jennah Bawa. The Foreign Office had lowered the British toll to five on Thursday after it emerged that one of those previously identified as British was Kenyan.