Israeli forces attacked an Islamic Jihad training camp in the southern Gaza Strip on Saturday, killing at least five people, officials on both sides said.
The strike in Rafah, a town on Gaza's border with Egypt, followed a Palestinian rocket salvo on Thursday which landed deep in Israel but caused no casualties.
Doctors and officials from Gaza's ruling Islamist Hamas said five people died in an explosion in the camp, and two others were hurt. Witnesses saw Israeli helicopters overhead.
In Jerusalem, an Israeli military spokesman confirmed there had been an attack but did not immediately elaborate.
Islamic Jihad, a sometime Hamas ally, has chafed at recent efforts by the more powerful faction to impose de facto ceasefires with Israel.