Witnesses to the first incident said gunmen shot and killed the men, aged 21 and 25, after they had confessed to collaborating with Israeli intelligence.
They said the gunmen played a videotape of the confessions to residents of the Tulkarm camp before executing the suspects in the street.
In the West Bank city of Nablus, medical officials said a 15-year-old activist from the al-Aqsa Martyrs Brigades, a group linked to Palestinian President Yasir Arafat's Fatah movement, died of wounds sustained in a mysterious car explosion on Wednesday night.
Palestinian security officials said the blast, which wounded two other people, may have been caused when a bomb detonated prematurely.
But the officials did not rule out sabotage by Israeli intelligence. Israeli military sources denied responsibility.