The Israeli army denied any involvement in the death on Saturday of Khalid Abu Sita, a senior leader of the Abu al-Rish Brigades, who was killed when his car blew up as he drove at night between the southern Gaza cities of Khan Yunus and Rafah.
Palestinian security sources and members of the Abu al-Rish Brigades said an Israeli missile fired from an unidentified aircraft hit Abu Sita's car.
The Abu al-Rish Brigades said they would avenge Abu Sita's death.
Abu Harun, a spokesman for the group, which is linked to the mainstream Fatah faction, said: "We do not forget the blood of our martyrs and our reaction will be strong and painful."
The Israeli army, which often admits to strikes on fighters' cars, denied involvement in the incident.
"The Israel Defence Forces was not involved in this incident," an army spokeswoman said.
Israel has said it will track down and kill those behind rocket attacks carried out by groups in Gaza including the Abu al-Rish Brigades. On Wednesday, it assassinated four fighters in the Gaza Strip in an attack on their car.
Members of the Palestinian resistance groups had been killed occasionally when explosives they transported detonated prematurely.
Earlier on Saturday, fighters launched two rockets at an Israeli farming community near Gaza, and the Israeli army responded by firing artillery shells towards open fields in northern Gaza.
Nobody was hurt in either incident.
Israel withdrew from the Gaza Strip in September after a 38-year occupation.