At least four people were killed today by a suicide bomb blast in the Afghan capital, Kabul. It happened in a crowded park opposite a clinic often used by foreign forces. Television pictures of the blast site showed a motorcycle overturned in the middle of a main road. The blast took place just two days before dozens of foreign ministers including U.N. Secretary General Ban Ki-moon and U.S. Secretary of state Hillary Clinton were due in the capital for the international conference of Afghanistan's future. Security has been tightened across Kabul ahead of the conference on Tuesday.