An Afghan mob infuriated by a Florida pastor's burning of a Koran last month stormed United Nations offices and killed up to 20 staff members, beheading two of them. After noon prayers, hundreds of demonstrators poured out of mosques and headed to the U.N. headquarters in the northern Afghanistan city of Mazar-i-Sharif. After disarming the guards, they stormed the compound. A police spokesman said 27 people have been arrested so far in connection with the attack. Tolo TV news in Kabul reported that the director of the U.N. mission in the city was among those killed, but that hasn't been confirmed. The crowd was angry over Florida pastor Terry Jones' burning of a Koran on March 20. Jones had garnered international attention for threatening to burn a Koran last September 11, then promised not to, but went ahead and burned a copy last month.