A Hamas spokesman told United Press International two of the dead were field commanders of al-Qassam Brigades, the group's military wing. He identified them as Ibrahim al-Diri and Amer Hassan.
The spokesman said the Al-Qassam Brigades had pledged that "the killing of our three mujahideen (Muslim strugglers) will not go unpunished."
The Palestinians died Wednesday when an Israeli Apache helicopter attacked their car near the Jewish settlement of Nitzarim.
Palestinian witnesses said they heard two explosions, then saw fire, dust and black smoke come out of the car.
Medics at Shiffa Hospital said at least six people were injured by shrapnel and two were in serious condition.
Earlier, Israeli soldiers killed an armed Palestinian youngster in the Tul Karem refugee camp in the West Bank.
Israel Radio reports the youth was a member of the al-Aksa Martyrs Brigades, part of Palestinian leader Yasser Arafat's Fatah Party, and had approached the soldiers, armed with an assault rifle.