IDF tanks and IAF warplanes attacked a series of targets throughout the Gaza Strip on Thursday, killing at least seven people, including three civilians, and wounding more than 20 others. Most of the casualties were caused in the morning, before Palestinians fired a a Katyusha rocket attack on Ashkelon. The rocket, which was fired from the northern Gaza Strip and landed in northern Ashkelon Thursday morning was a 122mm Grad Katyusha. It was launched from a distance of 16.5 kilometers and was the first projectile fired from the Strip that landed so far north. It landed in a open area and did not cause any casualties or damage. In one incident in Gaza, an IDF tank shell struck the home of a terror operative in the southern town of Khan Younis, killing the man as well as his sister, mother and brother. The army said troops had fired at gunmen who were shooting at them from houses. After the Katyusha attack, the IDF announced that it had targeted three buildings, one of them a weapons storehouse inside Gaza City, another a building belonging to a top Islamic Jihad man in the central Strip. The third target was a building belonging to Hamas in southern Gaza, the army said. Earlier, IDF forces, including 10 tanks, operating east of Khan Younis, skirmished with Hamas and Islamic Jihad militants, witnesses said. When troops became trapped in one area, IAF aircraft fired at least nine missiles, the witnesses said. Two operatives were killed and nine wounded in the air-strikes, doctors said. During the effort to save the troops, tanks fired heavy machine guns, and three children were injured, one critically, witnesses and doctors said. A Hamas militant was also killed in the fighting, Palestinian officials said. The fighting came days before US President George W. Bush is scheduled to arrive in the region, and Palestinian officials said Israel's ongoing military activity in Gaza threatened to undermine the president's visit. "We consider what's going on in Gaza ... as a bloody Israeli message in which Israel shirks itself of any commitment before the arrival of President Bush to the region," said Nabil Abu Rdeneh, a spokesman for President Mahmoud Abbas. "They are killing the spirit of the Annapolis conference." Israel said that the Katyusha rocket on Ashkelon marked an escalation that could not be tolerated. "The Palestinians have attacked a major Israeli city ... and thus have upped the ante," government spokesman David Baker said. "Israel will not allow any cities to be attacked by Palestinian rocket fire." Islamic Jihad and the Popular Resistance Committees, which are responsible for most rocket fire, claimed responsibility, pledging to strike even further into Israel. "We are going to launch more strikes in the depth of the entity," they said in a joint statement. Meanwhile, in the West Bank on Thursday, the IDF raided the city of Nablus with at least 50 jeeps in its largest operation there in about four months. Palestinian security forces have deployed around the city of about 150,000 in recent weeks, trying to impose order in the community known for anti-Israeli activity. In the IDF operation, troops imposed a curfew on Nablus' center, preventing most shops from opening and prompting most children to stay home from school, witnesses said. The army said soldiers were searching for operatives.