Sappers who examined the shells said some of them contained phosphorus, which is banned for use by international law. Officials are also looking into the possibility that a Qassam rocket was fired as part of the barrage.
No injuries or damages were reported in the attack.
Meanwhile, Israel's delegation at the United Nations filed a letter of complaint with the UN secretary general and with the current president of the Security Council, following the Jerusalem bombing and the ongoing rocket and mortar attacks from Gaza.
"I write to express my grave concern in the face of a very serious escalation of Palestinian terrorist attacks targeting innocent Israeli civilians, which threatens to undermine stability in our region," Israel's UN Ambassador Meron Reuben wrote.
"In the past week, we have witnessed the launch of some 63 mortar shells and four rockets from the Gaza Strip into Southern Israel, which represents an unprecedented increase in the projectile fire emanating from the Gaza Strip since the end of Operation Cast Lead in 2009," he wrote. "As I write this letter, terrorists in the Gaza Strip continue to fire mortars and rockets at Israel."
Early Wednesday, terrorists fired two long-range Grad rockets at Beersheba. Late Tuesday, a similar rocket was fired at the southern town of Ashdod.
Yitzhak Benhorin contributed to the story
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