The two men were shot by Israeli troops in broad daylight on Thursday in Haifa Street, in downtown Jenin, the sources said.
According to an AP report, the two men were driving through Jenin when four armed men jumped out of a car that had been parked for several hours and shot the men, the witnesses said. Their vehicle was riddled with gunfire.
Palestinian security sources identified the men as Mohammed Zaid and Ahmed Abahri, both 18 and members of the al-Aqsa Martyrs' Brigades, affiliated with the ruling Fatah party.
There was no immediate comment from the Israeli army.
The latest deaths brought to 4887 the number of people killed since the start of the second Palestinian intifada in September 2000.
More than three-quarters of the victims are Palestinians.