An Israeli air strike in Gaza killed three Palestinian civilians on Wednesday, including a 13-year-old boy, according to witnesses and medics, in what a spokeswoman for the Israeli military acknowledged was an attack on the wrong car.

Palestinians inspect a car destroyed in an Israeli air strike on Wednesday in the Gaza Strip. Witnesses said the victims, including a 13-year-old boy, were all members of the same family. ((Abid Katib/Getty Images))

The boy's father and uncle were also killed in the missile strike near Gaza City, according to witnesses.

The military spokeswoman said the vehicle was hit "in error" and an investigation has been launched into the incident. Israeli newspaper Haaretz reported sources within the Israeli military saying the missile was intended to strike a car carrying militants who were targeting Israel with rockets.

Meanwhile Wednesday, Israeli forces shot dead a leader of the militant Islamic Jihad group in the West Bank.

The deaths came as Palestinians held a general strike in the Gaza Strip and the West Bank to protest almost daily Israeli incursions and air strikes into Gaza.

Such Israeli operations are aimed at halting militant rocket attacks launched from the territory into southern Israel. On Wednesday, at least 28 Qassam rockets were fired into southern Israel, Haaretz said, but no injuries were reported.

On Tuesday, at least 19 Palestinians, including three civilians, were killed in air strikes and gun battles between militants and Israeli troops, according to Palestinian medical officials, in some of the worst violence to hit the region since Hamas seized control of Gaza in June.

No truce or prisoner exchange: Hamas leader

The bloodshed has threatened to derail peace negotiations between Israeli officials and a Palestinian negotiating team comprised of Fatah members. Palestinian President Mahmoud Abbas has condemned Tuesday's violence as "a massacre."

Hamas, which has been shunned by the international community since its victory in Palestinian parliamentary elections for its refusal to renounce attacks against Israel, has condemned Abbas for taking part in negotiations while the violence continues.

The militant movement took control of Gaza following intense fighting with forces loyal to Abbas's Fatah faction, to which Abbas responded by dissolving the fractured Fatah-Hamas coalition government.

Speaking Wednesday from Damascus, Syria, exiled Hamas leader Khaled Mashaal told reporters that Israel's military operations in the coastal strip made Hamas less likely to negotiate any truce with the Jewish state or release Gilad Shalit, an Israeli soldier the group has held captive since 2006.

"Palestinians' blood won't save Israel's leaders, but will drown them," Mashaal said. "What you are doing will deny you of any plan you could be betting on: No exchange for Gilad Shalit and no truce."