Missile warning sirens sounded for several minutes in southern and central Israel early Saturday, and the continuous boom of the launches could be heard in the Gaza Strip, Reuters and AFP reported. Gazans said they heard gunfire along Israel’s separation fence near the southern city of Khan Younis and saw large movements of armed militants.

The Israeli army announced on Saturday morning that an “unknown number of terrorists” from the Gaza Strip had infiltrated into Israel.

Israel’s emergency services said crews had been dispatched to areas of southern Israel near Gaza and that residents had been warned to stay indoors, but there were no details on any casualties.

Prime Minister Benjamin Netanyahu’s office said he would meet with senior security officials in the coming hours.

Neither Hamas, the Islamist movement that controls Gaza, nor Islamic Jihad, a smaller organization that has also fought several wars with Israel, claimed responsibility for the attacks. Islamic Jihad just celebrated its 36th anniversary.

In May, Israel launched an offensive against Palestinian Islamic Jihad in the Gaza Strip, sparking a five-day war between the Israeli army, Islamic Jihad and other armed groups in the territory that left 34 Palestinians and one Israeli dead.

At that time, more than a thousand rockets were fired from the Gaza Strip towards Israel, most of which were intercepted by the Israeli air defense system.

For its part, Israel has increased airstrikes in a small area. Hamas, which seized power in Gaza in 2007, has not been involved in the conflict since the spring.