Two senior Palestinian militants were killed in an Israeli air strike in the northern Gaza Strip, the Palestinian interior ministry has said.
Israel has targeted several senior Palestinian militants in Gaza
Missiles destroyed the jeep carrying the two men as it travelled through the Jabaliya refugee camp in northern Gaza on Tuesday.
At least five other Palestinians were also wounded in the strike.
Israeli warplanes have attacked cars carrying Palestinian militants in northern Gaza twice in the past week.
Hassan Madhun, a senior member of the al-Aqsa Martyrs' Brigades, an offshoot of the mainstream Fatah party, was killed by the strike.
The Israeli army confirmed they had targeted Madhun, who they believe was involved in the double suicide bombing that killed 10 Israelis in the port of Ashdod in March.
The second casualty was Fawzi Abu al-Qara, a leader of Hamas's military wing, the Izz al-Din Qassam brigades, in Jabaliya.
A spokesman for Hamas said Israel would "pay a heavy price for their crimes".
"This is an open war," Mushir al-Masri told the AFP news agency.
The BBC's correspondent in Gaza, Alan Johnston, believes the killing of the Hamas leader may be significant, because the group may now be drawn into a bout of violence it has so far avoided.