Two teen-age brothers were killed in the central Gaza Strip on Monday when an explosive device went off, Palestinian police said. A preliminary IDF response said Israel was not involved in the explosion, and that it was a possible work accident. The explosion took place in a small valley east of the Bureij refugee camp near Gaza's eastern border. The Israeli border is some 4 kilometers (2 miles) away. Palestinian police said their initial investigation showed that the two brothers, aged 15 and 16, were playing in the valley when the device exploded. It wasn't clear if the teens were handling the object or had stepped on it, police said. The boys were alone in the valley at the time of the blast, police said. Security forces were searching the area for other suspicious objects or clues to the blast.