British Foreign Secretary Margaret Beckett condemned on Wednesday the previous day's botched IAF missile strike on a car driving in the crowded Jabalya refugee camp in the northern Gaza Strip that killed three Palestinian children. "I was gravely concerned to hear of the death of three children in Gaza on 20 June, as well as a number of civilian injuries, as a result of an Israeli Defence Forces airstrike. I send my deepest condolences to their families," said Beckett. "As I have said before, the killing of innocent civilians, and particularly children, is completely unacceptable. The continuing violence on both sides, and the tragic death of a number of children and civilians in Gaza and West Bank in recent weeks, is making the prospect of a negotiated, peaceful resolution more distant," aded the foreign secretary Becklett strongly urged maximum restraint by the IDF to avoid further escalation of an "already very tense situation." "We call on the Israeli authorities to respect their obligations under international law and ensure that civilians, particularly children, are not harmed. In addition we call for an immediate halt to all rocket fire from the Gaza Strip on Israeli targets." An additional 13 Palestinians were wounded in the missile strike, which the IDF said had targeted an Aksa Martyrs Brigades terror cell. Senior Aksa Brigades operatives Amad Abu Hamed, who was the target of the attack, evaded the strike by jumping out of the way in the last minute. Still, he was lightly wounded in the attack. The IDF said that the targeted cell was responsible for launching three rockets at Sderot earlier in the day. [For a Jerusalem Online video of events click here] According to the IDF, Abu Hamed was in charge of the terrorist organization's relations with Hizbullah, and was in the midst of planning terrorist attacks at the Karni crossing. He was behind the smuggling of large amounts of weaponry into the Gaza Strip from Egypt. In response to the strike, al Aksa Martyrs' Brigades declared war against Sderot, urging its operatives to launch rockets at the city. "The reprisal is coming soon," said Abu Qussa, spokesman the Aksa Martyrs' Brigades. Abu Qussa said the revenge attacks could be anywhere and called on other militants to strike as well. "We will strike against the enemy everywhere," an Aksa Brigades flier read, "The Palestinian organizations must increase the attacks against the occupiers and declare war on Sderot and the other Zionist settlements." The dead were identified as five-year-old Muhammad Roka and two girls aged seven and 16, said Dr. Jumma Fatah of Shifa Hospital in Gaza City. A high-ranking IAF officer said that, while the military regretted the harm caused to innocent civilians, Israel was at war and would continue to target terror cells even in populated areas. "The Palestinians launch rockets from urban areas, and therefore we need to hit them there," the officer said. He said that the air force had invested a great deal of resources and effort in minimizing collateral damage during air strikes, even to the extent of cancelling targeted assassinations at the last minute after fears arose that innocent civilians might be hurt. Last Tuesday the IAF killed eight civilians alongside three Islamic Jihad terrorists in an air strike in Gaza City. In Tuesday night's air strike, the officer said, the targeted car was driving down an empty road and the air force did not foresee any civilian casualties when it launched the two missiles. Labor MK Ephraim Sneh told Army Radio Wednesday morning, "Those who are operating within a population of 1.25 million people can't guarantee 100 percent success and that each time the forces won't hit innocent people. We didn't intend to do this." Abu Hamed served in the past as an officer in the PA police, and was also recently involved in trying to establish an infrastructure to kidnap Israelis to be used as bargaining chips for Palestinian terrorists in Israeli jails. Among the wounded were also five children, including a seven-year-old boy in serious condition. The car exploded on a narrow street in the crowded refugee camp. The front of the car was badly damaged, but the back remained intact. Hundreds of angry Palestinians gathered around the vehicle, shouting slogans. Khalil Roka, a cousin of the dead boy, said he was sitting in front of his car repair shop while the children played in front of the house nearby. He said he saw a red flash as the car exploded, and the children were hit. On Tuesday, six rockets were fired at Israeli targets in the western Negev. Security officials said that Defense Minister Amir Peretz intended to give a green light to the IDF in the coming days to launch a massive air operation against Hamas targets in the Gaza Strip. "The operation will happen," one official in Peretz's office said. "We do not care if there are 30 Kassams or six Kassams a day since our goal is to completely stop the rocket fire altogether." The IDF operation, sources said, would probably not include a ground incursion into the Gaza Strip but would mostly be carried out by the IAF in continuous air strikes. Speaking at the World Zionist Congress in Jerusalem on Tuesday, Prime Minister Ehud Olmert hinted at Israel's intention to escalate military operations on the Gaza front. Expressing his empathy for the residents of Sderot and the Negev, Olmert said: "No one knows the pain, the fear, and the uncertainty that you're feeling more than I do." "I know it is difficult and painful," he continued. "I feel for the father who sends his child to school without knowing where the next Kassam might fall." Olmert promised that Israel would take harsher measures than ever against any parties responsible for launching Kassams. "No one has immunity, no matter what he does or what group he's associated with." "Responsibility for the continued rocket fire against Israel lies on the shoulders of the Palestinian Authority and the Hamas government," the IDF said. "We are determined to continue targeting terror cells without considering with which group the terrorists are associated." Earlier Tuesday, PA President Mahmoud Abbas called on armed Palestinian groups to stop firing rockets against Israel, warning that they would be responsible for any Israeli retaliation, an official said. "Chairman Abbas called on all military groups in Gaza to stop launching rockets at Israel and to fully comply with the truce with Israel," said Abbas aide Nabil Abu Rdeneh. "Chairman Abbas holds any group and any faction that violates the truce fully responsible for the destruction and demolitions and victims that will result because of any Israeli imminent aggression." Also Tuesday, operations at the Gaza Strip's border crossing with Egypt were suspended briefly in response to a security alert in the area. European monitors at the Rafah crossing asked the Palestinians operating the passage to stop operations until the security alert was lifted, said Julio De La Guardia, a spokesman for the European monitors. The alert was withdrawn within 30 minutes, De La Guardia said. Receiving the same terror alert, the IDF closed the Kerem Shalom crossing into the Gaza Strip. Gil Hoffman and AP contributed to the report.