The latest attack came Friday morning as Israeli aircraft fired missiles east of Gaza City, killing four Palestinians, at least three of them Hamas militants, and wounding six people, Hamas and Palestinian doctors said. There was no immediate Israeli comment. Two other strikes followed but there was no word of any casualties, the doctors said.
Those strikes, a series of Israeli air attacks Thursday, and the reported movement of a handful of tanks a few hundred yards into the northern Gaza Strip, followed days of Hamas rocket barrages into Israel.
Street fighting between the Palestinian factions that has gripped Gaza since the weekend calmed under a truce agreement, but clashes still killed at least four people - a day after 22 died in the worst battles during a year of factional bloodshed.
There was no sign of any Israeli military buildup that would indicate plans for a serious intervention into chaotic Gaza, though a few tanks and soldiers moved just across the Gaza border. Israel's government said its attacks were intended solely to discourage rocket attacks on southern Israel.
"Israel will take every defensive measure to stop these rocket attacks. We will defend our citizens against the rockets, against the weapons, against the Iranian-backed Hamas who are attacking Israel," government spokeswoman Miri Eisen said.
Analysts said Israeli policy makers were likely trying to walk a narrow line to avoid uniting Palestinian factions into a common front against Israel.
Hamas mounted accusations on its Web sites, radio and TV that Abbas-linked forces were working with Israel - a charge dismissed as "absurd" by a Fatah spokesman.
Although Israel said it wasn't taking sides, the airstrikes did make it harder for Hamas gunmen to move around and that could help Fatah's fighters, who appeared to have been outfought in the latest round of battles. Hamas fighters have clearly been more motivated in the current fighting and earlier battles in December.
In Washington, State Department spokesman Sean McCormack said Israel had shown "great restraint" in exercising its right to self defense and warned Hamas it would never achieve a Palestinian state unless it chose peace and worked with Fatah.
"They're not going to see it by launching Qassam rockets into Israel. They're not going to see it by attacking the legitimate security forces of the Palestinian Authority. They're not going to see it by sending young people armed with suicide vests to blow up other Israeli youngsters," McCormack said. A day after bombing two Hamas targets, Israeli aircraft struck a Hamas command center, a trailer housing bodyguards and two vehicles Thursday, citing the firing by militants of more than 50 rockets at the Israeli border town of Sderot over three days. Busloads of Sderot residents sought shelter away from the frontier. Israeli media said more than 2,000 of the town's 24,000 people had left. Thursday's airstrikes came on the fifth day of factional fighting that appeared to be tearing apart a Hamas-Fatah unity government formed two months ago in hopes of ending such clashes and also killing any hope of renewed peacemaking between Israel and the Palestinians. In all, 46 Palestinians had been killed by the infighting since Sunday. But street clashes ebbed Thursday and Gazans who had been trapped in their homes the previous day hurried out to stock up on bread, bottled water and other supplies. "I have run out of cigarettes and I'm almost out of mineral water. I don't have many diapers left," said grocer Ghassan Abu al-Qas. No one stayed outside long, though, fearing a resumption of fighting. Few cars and trucks ventured out. Israel's airstrikes complicated an already chaotic situation in Gaza, making the embattled Abbas even more vulnerable to Hamas accusations that he is in Israel's pocket. With his aides citing security concerns, Abbas canceled a Thursday trip to Gaza for talks with Prime Minister Ismail Haniyeh of Hamas. Israel had remained on the sidelines during the infighting, but security officials said the military had to respond to the rocket attacks on Sderot. Israeli Prime Minister Ehud Olmert was under intense public pressure to respond to the Hamas barrage, and he visited the town late Thursday to tell residents they shouldn't feel alone, his office said. "I am handling this crisis in order to remove this threat as much as possible," he was quoted as saying. During his visit, the rocket alert system sounded, but an official did not know if a rocket hit. Olmert is fighting for political survival in the face of plummeting popularity and harsh criticism of his handling of last summer's war in Lebanon. Still, he Olmert probably would be wary of a major ground offensive in Gaza, fearful of another inconclusive effort. Israeli attacks have unified Palestinians in the past. "It makes Hamas look like it is the one that is under attack from the so-called American-Israeli team within Fatah," Palestinian analyst Yehia Rabah said. Israeli analyst Yossi Alpher said intervening would be fraught with risk for Israel. "If the attacks are seen by the Palestinians as being very comprehensive, they will enable Hamas to rally everyone around the cause of opposing Israel," he said. Hamas reacted to the airstrikes by loosing a barrage of verbal attacks on Fatah. Hamas lawmaker Salah Bardawil said Israel and Fatah had a "shared interest in striking at Hamas' strength" and that Fatah was led by a "bunch of mercenaries." Fawzi Barhoum, a Hamas spokesman, said the group's opponents are "pro-Zionist and pro-American elements who are working in a systematic, barbaric pre-planned campaign against Hamas and its elected leadership." A Fatah spokesman, Maher Mikdad, said the accusations were "absurd" and were designed to deflect criticism in light of "public discontent and rejection" of Hamas' militant action. "Israel's interference is only in the interest of Hamas," he said. In the biggest Israeli strike of the day a bomb hit a two-story building belonging to Hamas' militia, the Executive Unit, destroying it and several nearby structures. The blast killed a militant and wounded 45 people, including civilians, who were dug out of the rubble by a frantic crowd. Later, Israeli missiles struck a trailer housing bodyguards of a Hamas official and a car carrying two senior Hamas militants, killing two people. An Israeli hit on a pickup truck near the southern Gaza town of Rafah killed a father and his two teenage sons. Israel's military said it targeted a rocket squad, but Palestinians said that was apparently a case of mistaken identity after Hamas fired rockets from the area. Late at night, Israel said it staged an air attack on a member of a Palestinian rocket squad in Gaza City. His condition was not known. Palestinians said five Israeli tanks moved about 200 yards into northern Gaza, in an area where Israel's troops have operated in the past trying to quell rocket attacks. Israeli media said a few soldiers set up observation posts. The army had no comment.