The White House has said it is concerned about attempts by Somalia's al Shabaab to recruit in the US, but has no confirmation that any American citizens were involved in the deadly siege at a shopping mall in Kenya.
The Somali militant group with ties to al Qaeda has claimed responsibility for the three-day stand-off in Nairobi in which at least 62 people have died.
Kenya Foreign Minister Amina Mohamed said "two or three Americans" were involved in the attack, along with one British woman.
Ms Mohamed said the Americans were 18 or 19 years old, of Somali and Arab origin, and lived "in Minnesota and one other place".
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