The IAF on Thursday bombed a building in the Jabalya refugee camp in Gaza, reportedly killing seven people, including senior Hamas leader and cleric Sheikh Nizar Rayyan, and injuring thirty others. Army Radio reported that according to Palestinian sources, his family was warned before the attack but did not leave the building. Earlier, the IAF launched a quick-fire response shortly after a Grad-type missile slammed into the top floor of an Ashdod building. The army said that the air force struck both the Gaza terror cell that launched the projectile and the launching device. Several Hamas homes which were used to store weapons were also bombed in the afternoon air raid. Since Thursday morning, the IAF struck over 20 targets, including rocket launching sites in northern Gaza, as well as tunnels and a car in the southern Gaza Strip, killing several Hamas operatives. In addition, the IAF bombed the homes of three senior Gaza terrorists. One of the homes belonged to Mohammad Baroud, a top Popular Resistance Committees operative. The army said that Baroud was the head of all rocket cells in northern Gaza and that he was funded and supported by Hamas. The army said that there were anti-tank missiles, rockets and bombs in the home. Another of the homes destroyed belonged to Hasim Drili, a northern Gaza Hamas operative. The army said that he had a manufacturing plant in his home for rockets, mortar shells and missiles. The third home belonged to Tafik Abu Raf, a Hamas terror operative in the central Gaza Strip. The IDF said that he had a weapons laboratory in his house. Not including Thursday's strikes, IAF warplanes have carried out some 500 sorties against Hamas targets, and helicopters have flown hundreds more combat missions in five days of raids, a senior Israeli military officer said Wednesday on condition of anonymity in line with military regulations. More than 400 Gazans have been killed and more than 1,600 have been wounded since the start of the Gaza operation, Gaza health officials said. The UN said the Gaza death toll includes more than 60 civilians. Meanwhile, IDF Infantry, Engineering Corps and Artillery Corps troops, as well as thousands of reserve soldiers, were awaiting an order to cross into the Strip in the event of a ground operation. The IDF said the imminent military action would be limited, but that it would involve a large number of ground forces, Israel Radio reported. Military spokeswoman Maj. Avital Leibovich said preparations for a ground operation were complete. "The infantry, the artillery and other forces are ready. They're around the Gaza Strip, waiting for any calls to go inside," Leibovich said. Also Thursday, government officials said that Israel was demanding international monitors as a key term of any future truce with Gaza factions. Prime Minister Ehud Olmert, who rebuffed a French proposal for a two-day timeout, won't agree to a truce unless international monitors take responsibility for enforcing it, the officials said. He had made this point in talks with US Secretary of State Condoleezza Rice and other world leaders who are pressing for an end to the violence, they added. They spoke on condition of anonymity because the talks were confidential. The idea was floated before the offensive but did not gain traction because of the complications created by the existence of rival Palestinian governments in the West Bank and Gaza, defense officials said.