Palestinian officials on Monday showed fragments of what they said was a missile that hit a car outside Nablus's Balata refugee camp, killing the local leader of the al-Aqsa Martyrs Brigades, Khalil Marshud, and another member of the group.
The missile left a large crater in the road, they said. The Israeli army declined to comment.
The identity of the second Palestinian, in the car alongside Marshud, was not immediately known.
The deaths bring the toll since the September 2000 start of al-Aqsa Intifada, or uprising, to 4105, including 3114 Palestinians and 920 Israelis.
Israeli helicopter gunships fired missiles at a car in Nablus on 3 May, killing three members of the al-Aqsa Brigades, who were in the vehicle. Palestinian security sources said Marshud was the target of that attack but escaped because he was in a different vehicle.