Lebanese security officials said a bomb has exploded on a busy street in the northern city of Tripoli, killing at least three people and wounding many. The officials said the target was a military bus in the central Nour Square. They said Wednesday's explosion happened as the streets were filled with people heading to work, causing many injuries. The officials spoke on condition of anonymity for not being authorized to speak to the media. Tripoli has witnessed sectarian clashes in the past weeks that killed and wounded dozens of people. The city is also close to the Palestinian refugee camp of Nahr el-Bared, which experienced deadly clashes last year between Lebanese troops and members of the al-Qaida -inspired Fatah Islam group.