The Israeli army said troops had spotted three men crawling towards the border fence and had shot at them after they refused calls to stop, did not identify themselves and ignored warning shots fired in the air.
An army spokeswoman could not confirm whether the three men were armed or if their actions were hostile.
Palestinian medics said the three men had come from a refugee camp in the central Gaza Strip but did not know whether they were members of a resistance faction.
Israel has declared areas close to the border fence in the northern part of the costal territory, which fighters have used to fire rockets into Israel, as a no-go area for Palestinians and has used artillery and helicopter gunships to enforce this.
Palestinians have condemned the buffer zone as a re-occupation of land evacuated by Israel last year.