CAIRO - A follower of Islamic State was responsible for an attack last week on a Kenyan police officer outside a US embassy in Nairobi, the group's Amaq news agency said on Saturday.A knife-wielding man whom police described as a criminal was shot dead outside the US Embassy in Nairobi last Thursday after he attacked and injured a Kenyan police officer."The person who carried out the stabbing of a guard outside the American embassy in Nairobi last Thursday was a soldier of Islamic State responding to calls to target coalition countries," Amaq said.