Palestinian militants from the Gaza Strip burst into southern Israel on Wednesday and attacked a fuel depot, killing two Israeli civilians in a daring daylight raid that threatened to set off a new round of fighting.

Two attackers were killed as troops returned fire, but two others fled back into Gaza, the military said.

Israel rushed forces and tanks across the border into northern Gaza after the raid, and Israeli aircraft struck a car carrying militants near Gaza City. Six people were killed in the Israeli reprisals.

Islamic Jihad and two other smaller armed factions, the Popular Resistance Committees and Mujahedeen Brigades, claimed responsibility for the raid at the Nahal Oz border terminal, just over Israel's border with Gaza. But Israeli government spokesman Mark Regev said Gaza's Hamas rulers were "responsible and will be held accountable."

The Popular Resistance Committees has close ties with Hamas, and a Hamas spokesman praised the attack. The Mujahedeen Brigades is an offshoot of Palestinian President Mahmoud Abbas' Fatah party.

Islamic Jihad spokesman Abu Ahmad called the raid a "unique and complicated operation."

Maj. Tal Levram, an Israeli army spokesman, said shortly after 3 p.m. four Palestinian attackers crossed through the border into the depot and riddled the bodies of two civilians with bullets.

He said the militants fired a series of mortar shells before the infiltration to divert Israel's attention. The mortar attacks continued afterward, and one landed by Levram as he detailed the attack.

He said Israeli troops jumped to the scene within minutes and managed to kill two of the attackers, while two other escaped.

He said the army believes the militants were planning to stage an attack on a kibbutz or to kidnap a soldier, but were thwarted by the army's quick response.

"It could have been much much worse," he said.

The depot was not damaged, sparing Gaza's civilian population further hardship. Plumes of smoke billowed up from the depot, the sole conduit of fuel to Gaza's 1.4 million residents. Israel cordoned off the area, and police and emergency service reinforcements were rushed there.

"The Hamas attack on the fuel terminal that supplies Gaza its energy shows their total and complete disregard for the civilian population of Gaza," Regev said. "Unfortunately, Hamas is holding hostage to its extremist and hateful agenda the civilian population of both the Gaza Strip and southern Israel."

Gaza has already been facing fuel shortages as a result of Israeli sanctions.

The gas flow was temporarily stopped after the attack and Israeli Cabinet Minister Gideon Ezra told Israel's Channel 2 TV that Israel should stop transferring fuel altogether.

Residents of nearby Israeli border communities hunkered down in their homes, even after the violence subsided.

"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 adjacent to the depot.

Israeli aircraft struck outside Gaza City shortly after the raid. Islamic Jihad said one gunman was killed in the air attack. Tank fire in the area killed three civilians, one militant and wounded 10, Palestinian hospital officials said.

Two other militants were killed in airstrikes.

Munther Rahmi, a worker on the Palestinian side of the border, said he saw Israeli tanks crossing into Gaza. "We are surrounded by tanks. It's a war out there," he said.

Fawzi Barhoum, a Hamas spokesman, praised the attack as "heroic and courageous." He said Hamas was not responsible but affirmed his group's support for "resistance."

The attack upset a recent period of calm in the area that followed a broad Israeli military offensive that killed more than 120 Palestinians, including dozens of civilians. Since the offensive ended in early March, Egypt has been trying to mediate a cease-fire between Israel and Hamas.

Although violence had subsided, tensions have been increasing in Gaza, whose 1.4 million residents have been confined to the territory since Hamas wrested control there in June.

On Tuesday, Hamas threatened to burst across the Israeli and Egyptian borders to end Israel's blockade of Gaza, imposed after the militant group's takeover.

Egyptian troops went on alert Wednesday Gaza, fearing Hamas militants may attempt to forcibly breach its border.

In January, Hamas militants blew holes in the border partition, allowing hundreds of thousands of Palestinians to stream into Egypt unchecked for ten days.

Earlier Wednesday, a Hamas militant and an Israeli soldier were killed in clashes in southern Gaza. The military said it launched a brief ground operation and airstrikes there in response to shooting attacks and other anti-Israel activity.

Last week, an aide to Israel's public security minister was wounded by a Palestinian gunman as he and the minister toured an observation point overlooking Gaza with a group of Canadian tourists.

Wednesday's raid came at the tail end of a five-day nationwide civil defense drill, meant to test Israel's response to war and other emergency situations.