"The IDF's response today was not a response to an incident in which an IDF soldier was killed and three injured. Israel's response to this incident will come," Prime Minister Ehud Olmert said Tuesday during a meeting with ministry heads in Jerusalem. The prime minister was referring to the ambush of an IDF patrol near the Kissufim crossing on the Gaza border earlier in the day. One soldier was killed and three others were wounded in the attack. "We didn't say this ceasefire fragile for nothing. Israel did not sign an agreement with Hamas, but decided to cease its fire unilaterally. This allows us the maneuvering space to respond to such incidents." Defense Minister Ehud Barak and Foreign Minister Tzipi Livni joined Olmert's assessment that the attack constitutes a stark violation of the conditions under which Israel agreed to hold its fire, and the they appear to agree that a harsh military response must be carried out. The three are scheduled to discuss the new development Wednesday, immediately following the security cabinet meeting. The roadside bomb is detonated (Video: Reuters) "The prime minister has warned on more than one occasion over the course of the past week that the ceasefire is fragile and that we must continue to monitor it," a senior official told Ynet. "Israel will not restrain itself after such a blatant provocation." Meanwhile ministers are expecting US President Barack Obama's envoy to the Middle East, George Mitchell, who is scheduled to arrive Wednesday. He is slated to meet with Olmert, Barak, Livni, and President Shimon Peres. Mitchell's presence may be a possible tempering influence on Israel's military response to the Kissufim attack, as the envoy is seeking to stabilize and solidify the ceasefire. Barak is scheduled to leave Wednesday for Washington, where he is set to meet with US counterpart Robert Gates. Due to the recent security developments the trip has been called into question, but the Defense Ministry says that the visit will proceed as planned.