The authorities in Nigeria say, they have arrested two members of the Islamist group Boko Haram in connection with last week's bombing of the United Nations headquarters in the capital, Abuja. Boko Haram said it carried out a suicide attack which killed more than 20 people. The state security service said the attack had been mastermined by what it described as a notorious member of Boko Haram who had recently returned from Somalia and was linked to Al-Qaeda.