Three Gazans were killed on Tuesday in a mysterious blast at a training camp used by militants of the Popular Resistance Committees near the Egyptian border, medics told AFP. \"Three martyrs were killed and four others were injured in a blast in a site belonging to the Popular Resistance in the Tel Sultan neighbourhood of Rafah,\" said Adham Abu Selmiya, spokesman for the Hamas-run medical services in Gaza. The cause of the blast was not immediately clear, but the Israeli military told AFP it had \"nothing to do with the explosion.\" On October 20, 13 Palestinians civilians were injured by an explosion of undetermined origin in a Hamas security services building in Tel Sultan.