NAHAL OZ, Israel (AP) -- Militants from the Gaza Strip slipped across the border and opened fire at a fuel depot in southern Israel on Wednesday, killing two Israeli civilians in a brazen daylight raid that threatened to set off heavy combat after a monthlong lull.
The Israeli government held Gaza's Hamas rulers responsible for the attack and sent tanks, troops and aircraft into the Palestinian territory. At least nine Palestinians died during the day, including two at the depot and seven in Gaza.
Earlier in the day, a Hamas militant and an Israeli soldier also were killed in clashes in southern Gaza.
The surge in violence could jeopardize recently renewed peace talks between Israel and the Palestinian government based in the West Bank, and the raid on the depot posed a threat to the supply of fuel to Gaza.
The facility is the sole conduit of gasoline to the coastal territory. Officials said there was no serious damage despite plumes of smoke billowing from the site, but Israel already has reduced the flow of fuel to Gaza as part of its sanctions against Hamas, causing severe shortages and rationing.
Israeli Foreign Ministry spokesman Arye Mekel said the attack would only cause more harm to Gazan civilians by threatening the current flow of fuel and other humanitarian supplies to Gaza.
"Israel sends food, gas, medical supplies and humanitarian assistance every day and the terrorists who attacked the crossing today are trying to harm this operation and are harming mostly the well-being of the people," Mekel said.
Israeli officials said four gunmen climbed over a border fence while their comrades fired mortar shells into Israel to divert attention. The attackers entered the depot and riddled two workers with bullets.
Maj. Tal Levram, an Israeli army spokesman, said soldiers arrived within minutes and killed two of the militants, but the other two escaped. He said the raiders apparently also planned to attack a neighboring Israeli village or to kidnap soldiers, but were thwarted by the army.
"It could have been much, much worse," he said.
Residents of nearby Israeli border communities stayed hunkered down in their homes even after the attackers fled. There were sporadic mortar attacks into the evening. One shell heavily damaged an Israeli home and another landed about 100 yards from journalists. The army said one soldier was wounded in the hand by Palestinian sniper fire.
"The army told us not to leave our homes, not to get out of the house," said Moran Freibach, 37, a resident of Kibbutz Nahal Oz, a farming community next to the fuel depot.
Israeli airstrikes targeted militants in Gaza late into the night.
Islamic Jihad, an armed extremist group backed by Iran, and two smaller militant groups claimed responsibility for the raid. Islamic Jihad spokesman Abu Ahmad called it a "unique and complicated operation."
Palestinian militants frequently attack Israeli targets along the border, but they rarely succeed in getting across the wall.
In December, two militants were gunned down by Israeli soldiers after crossing over and attacking an army base. In the most serious attack, militants tunneled into Israel in June 2006, killed two soldiers and captured a third. The soldier, Cpl. Gilad Schalit, remains in captivity in Gaza.
Wednesday's attack upset a recent period of calm following a broad Israeli military offensive that killed more than 120 Palestinians in Gaza, including dozens of civilians. Since the offensive ended in early March, Egypt has been trying to mediate a cease-fire between Israel and Hamas, and the sides appear to have been honoring an informal truce.
But tensions have been increasing in Gaza, whose 1.4 million people have been confined to the territory since Hamas wrested control last June from security forces loyal to Palestinian President Mahmoud Abbas.
Israeli sanctions, which have caused shortages of fuel, electricity and basic goods, have hit the area hard. On Tuesday, Hamas threatened to blow up Gaza's border walls with Israel and Egypt to relieve the strain. Hamas breached the Egyptian border last January, allowing thousands of people to pour into Egypt for more than a week before the border was resealed.
Israeli Defense Minister Ehud Barak, who said Hamas was "responsible for the attack and will be held accountable," has repeatedly threatened a broad offensive into Gaza if attacks on Israel persisted.
Last week, an aide to Israel's public security minister was wounded by a Palestinian sniper as he and the minister toured an observation point overlooking Gaza with a group of Canadian visitors.
Though not directly involved in the fuel depot raid, Hamas has maintained a firm grip on power since violently taking over Gaza and most likely could have prevented Wednesday's attack. Fawzi Barhoum, a Hamas spokesman, praised the attack as "heroic and courageous."
Hamas could have its reasons for seeking a resumption of hostilities. It has expressed impatience with Egypt's failure to forge a cease-fire and repeatedly accuses the world of ignoring the plight of Gazans. A new round of fighting would draw attention to Gaza.
Islamic Jihad said the attack sent a message "that the Palestinian people will not be patient and will direct their anger against the siege toward the Zionist enemy."
The infiltration also serves as a reminder that Israel, which is conducting peace talks with Abbas, won't be able to implement a deal without Hamas' consent. Hamas might also be interested in disrupting Israel's upcoming celebrations marking 60 years of independence.
Abbas rules from the West Bank and wields little influence in Gaza. His government said Wednesday's raid would harm peace talks and make life more difficult for Gazans.
Mekel, the Israeli Foreign Ministry spokesman, said the raid would not affect peace negotiations, which resumed this week with a summit between Abbas and Israeli Prime Minister Ehud Olmert. The two sides hope to reach a final peace deal by the end of the year.
"We decided that we will continue to talk and will not let terrorists have a veto voice on the talks with the pragmatic forces," Mekel said.