JERUSALEM (CNN) -- Palestinian militants who infiltrated Israel from Gaza killed two Israeli civilians and wounded several others Wednesday, Israeli police and ambulance services told CNN.
The attack at the Nahal Oz border crossing happened after an intense barrage of mortar fire that led Israeli troops to believe that either a kidnapping attempt or an effort to infiltrate Israel was under way, an Israel Defense Forces officer who didn't want to be named said.
Four militants were involved -- two were killed and two escaped back to Gaza, the IDF officer told CNN.
The militants did not enter Israel through any of the tunnels at the border crossing, which is just outside Gaza City, the officer said.
The crossing, which is the main transit route for delivering fuel supplies to Gaza, normally is open from 7:30 a.m. to 3 p.m., but has been closed until further notice, he added.
The Popular Resistance Committees, Islamic Jihad and Fatah's al-Mujahedeen Brigades claimed responsibility for the operation, but Israel put the blame squarely on Gaza's Hamas leadership.
"This attack on the main energy supplier for the Gaza Strip demonstrates Hamas' total disregard for the well-being of the civilian population in Gaza," Israeli government spokesman Mark Regev said.
"Hamas is holding hostage the civilians of Gaza and the civilians of southern Israel to their extremist agenda," he said. "We hold them responsible and accountable."
A source in the Popular Resistance Committees said the aim of the joint operation was to abduct an Israeli soldier.
The attack happened hours after a predawn clash between the Israeli military and Palestinian militants in southern Gaza, which left an Israeli soldier and a Hamas militant dead.
Also Wednesday, Israel carried out a series of airstrikes in Gaza, including one that targeted a house east of Gaza City, killing three civilians, Palestinian security sources said.
Two other Palestinians were killed and four injured in airstrikes near Gaza City, including a field commander for the Islamic Jihad, the sources said.
An Israeli military spokeswoman confirmed one airstrike that targeted a car. She had no details on casualties. E-mail to a friend
CNN's Ben Wedeman contributed to this report.