IAF warplanes bombed a smuggling tunnel under the southern border of the Gaza Strip overnight Sunday, hours after Palestinians fired two mortar shells near the Erez Crossing, just yards away from ambulances that were transferring a Palestinian heart patient to Israel for treatment. The ambulances were parked back-to-back inside the crossing as the mortars landed. Sick Palestinians cross almost daily into Israel for treatment in Israeli and overseas hospitals. No casualties were reported in the airstrike, which was said to also be in response to a Kassam rocket attack earlier in the day. The Kassam had struck an open field near the Sdot Negev region. Neither the Kassam rocket or the mortar shells caused casualties or damage. "We are again witness to the way terror groups misuse the humanitarian services Israel offers the residents of the Gaza Strip," said Col. Moshe Levy, head of the IDF's Gaza Coordination and Liaison Administration, based near the Erez Crossing. "This type of attack, against a crossing that is used by the Palestinian civilian population, is first and foremost an attack on the weakest Palestinians - those who require medical treatments outside of Gaza," Levy added. Following Sunday morning's Kassam attack, opposition leader Tzipi Livni said that Israel must respond to every rocket. Speaking on a tour of Beersheba with Kadima faction members on Sunday afternoon, Livni said Israel must not "collect Kassams" before embarking on a military operation. The last Kassam attack was in mid-July, when a rocket also struck the Sdot Negev region. Since Operation Cast Lead, around 180 rockets and mortars have been fired into Israel. Prime Minister Binyamin Netanyahu has vowed to respond to any rocket fire from the Strip, saying in late July, "Our policy is that we are not prepared to accept rocket and missile fire on Israeli territory. For every rocket, before the elections [in February] there may not have been a response, but that has not been the case since the elections. This was and will remain our policy." Israel has recently conducted successful tests of the Iron Dome missile defense system. The system, under development by Rafael Defense Systems, is slated to become operational sometime in 2010 and is reportedly capable of intercepting short-range Kassam and Katyusha rockets fired by Hamas in the Gaza Strip and Hizbullah in southern Lebanon. Herb Keinon contributed to this report.