Israel launched air strikes on the Gaza Strip early Thursday, which Palestinian fighters reacted to by firing rockets in the latest bout of unrest in the region.
The overnight attacks -- which Israel's army confirmed in a statement at 02:41 am (0041 GMT) -- come hours after the army intercepted a rocket fired from the Palestinian territory.
Emergency services reported no immediate casualties on either side.
According to local security sources and witnesses, the first round of strikes -- at least seven -- hit a training centre of the Ezzedine al-Qassam Brigades, the armed wing of Hamas. The center is in the Al-Maghazi refugee camp in the central Gaza Strip.
A statement by the Israeli army said fighter jets had "struck a production site for raw chemical material production, preservation and storage along with a weapon manufacturing site" belonging to Hamas.
The strikes came "in response to the rocket launch from the Gaza Strip into Israel earlier" Wednesday.
After the strikes, AFP reporters and witnesses saw new rounds of rockets fired from Gaza, and fresh explosions could be heard from Gaza City around 3:15 am (0115 GMT).
Warning sirens sounded in Sderot, a town in southern Israel close to the Gaza Strip, according to the Israeli army.
