The Israel Defense Forces launched a series of air strikes overnight Thursday against targets in the Gaza Strip, hours after a Qassam rocket fired from the Strip hit southern Israel.

Three Palestinians were reportedly killed in the strike, including a 15 year-old boy, with two wounded and several others feared trapped inside the ruins, medics said.

Explosions reportedly rocked Gaza City, Khan Younis and Rafah, sending flames shooting into the air.

The IDF Spokesman's Office said Israel Air Force aircraft bombed four Gaza targets: a tunnel linking the Strip to Israel, a weaponry workshop in Gaza City and two smuggling tunnels linking the southern Strip to Egypt.

The Qassam launced at Israel Thursday exploded just south of Ashkelon, causing no casualties or damage. The rocket fire came at the heels of a barrage of mortar shells earlier in the day, with Gaza militants firing at least 10 shells into Israel, and an anti-tank missile being fired at Israel Defense Forces troops patrolling the border with Gaza.

No one was hurt in any of the incidents.

Earlier Thursday, the Israel Air Force dropped thousands of warning leaflets over Gaza, warning Gaza residents to stay away from the border with Israel and to avoid involvement in smuggling, Ma'an news agency reported.

One of the leaflets featured a map, and warns Gazans that anyone within 300 meters of the security fence is endangering himself.

Another leaflet urged Gazans not to sit idly by as smugglers put them and their communities in harm's way. It included a phone number and e-mail address for anyone willing to provide information about the smuggling tunnels.

The warnings came after six mortar shells exploded in the northwestern Negev, three others struck near the Kerem Shalom crossing with Gaza, while another exploded in the coastal strip.

The Popular Resistance Committees (PRC) claimed responsibility Thursday for the mortar fire.

The Defense Ministry on Thursday closed the Kerem Shalom crossing until further notice. Dozens of aid trucks that were prepared to deliver humanitarian supplies to Gaza were waiting at the crossing Thursday morning, Israel Radio reported.

On Wednesday, GOC Southern Command Yoav Galant warned Negev residents that the quiet Israel has recently expereinced along the Gaza border may only be temporary, adding that the IDF was prepared to face tensions should they arise.

Galant also urged civilians in the Negev to "prepare themselves for another round of fighting."

"It is important that we fully appreciate the value of this calm period for the residents of the area," he said. "The quietness allows the development of the regional infrastructure, agriculture and economical prosperity."

Hamas had said it was cracking down on militant groups firing at Israel from the Gaza Strip, but communities in the Negev have been hit with rockets numerous times in the year since the IDF embarked on Operation Cast Lead.

Just last week, the Popular Front for the Liberation of Palestine (PFLP) claimed responsibility for firing two Russian-made Grad missiles from Gaza at southern Israel.

The Popular Resistance Committees (PRC) also claimed responsibility for firing four mortar shells at Israeli army vehicles near the border the week before.

Prime Minister Benjamin Netanyahu threatened following those strikes that Israel would respond to every single rocket by Gaza militants.