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Four Britons dead in Kenya attack
Trucks of soldiers from the Kenya Defense Forces arrive outside the Westgate Mall in Nairobi, Kenya (AP)
Four Britons have now been confirmed among the scores killed when terrorists stormed a shopping centre in Nairobi.
The Foreign Office gave an update on casualties after Defence Secretary Philip Hammond chaired a meeting of the Cobra emergency committee in Whitehall.
David Cameron is returning to Downing Street to oversee the British response to the crisis, as Kenyan security forces attempt to clear the Westgate Mall and free any surviving hostages.
Mr Hammond said the UK was prepared to offer any help the Kenyan authorities required. He said: "We stand ready to provide them with any additional assistance they require. We will be monitoring the situation throughout the day and the Prime Minister will be returning to London to chair a further Cobra meeting later this afternoon."
Downing Street said that Mr Cameron, who has spoken to the Kenyan president Uhuru Kenyatta, had offered help in terms of "policing, intelligence collaboration and other related kinds" of assistance.
There were reports of multiple blasts and a barrage of gunfire at the mall. Black and grey smoke was seen rising up from the complex. Earlier the authorities said "most of the hostages" had already been rescued and the majority of the building had been secured in a major military operation - although that was later contradicted by sources at the scene.
The attack by Islamic extremists has left 68 dead and more than 170 injured, including many children. One of the Britons killed in the attack has been named in reports as Ross Langdon, who had dual nationality with Australia. The architect is believed to have died alongside his girlfriend who was heavily pregnant.
Somali-based militant group al-Shabaab claimed responsibility for the atrocity, which Mr Cameron described as an "absolutely sickening and despicable act of appalling brutality".
The Foreign Office is investigating suggestions that a female British terror suspect nicknamed the "White Widow" could have been linked to the plot. Witness accounts have suggested a woman was among the attackers, fuelling speculation that wanted Samantha Lewthwaite, who was married to July 7 bomber Jermaine Lindsay, was involved. She is wanted by Kenyan police over links to a suspected terrorist cell planning bomb attacks.
In March 2012 it was reported that Lewthwaite, 29, who is originally from Aylesbury, Buckinghamshire, had fled across the border from Kenya to Somalia. A Foreign Office spokesman said: "We are aware of the reports and we are looking into them."