JERUSALEM - Israeli troops shot dead two Palestinians in the West Bank early Sunday in separate clashes that erupted as they made more arrests in the hunt for three missing teenagers.Their deaths raised to four the number of Palestinians killed since the Israeli army began a massive search for three young students who disappeared on June 12 while hitchhiking in the southern West Bank. Israel accuses Hamas militants of kidnapping them, and has said the objective of "Operation Brother's Keeper" is to bring them home safe while dealing a crushing blow to the West Bank infrastructure of its Islamist nemesis.So far, the army has arrested more than 340 Palestinians, around two thirds of them Hamas members. The teens' seizure has been condemned by Palestinian president Mahmud Abbas, who on Sunday questioned why Israeli Prime Minister Benjamin Netanyahu had not condemned the bloodshed triggered by the manhunt. "I said the kidnapping was a crime, but does that justify the killing of... Palestinian teens in cold blood?" Abbas asked in an interview with Haaretz newspaper, referring to the deaths of two young Palestinians earlier this week. "What does Netanyahu have to say about the killings? Does he condemn it?"Abbas also said he has seen no concrete evidence of the Islamist group's involvement, saying: "I have no credible information that Hamas was behind the kidnapping." But Netanyahu insisted Israel had "unequivocal proof" that Hamas was behind the youths' disappearance. "Soon this information will be made public," he told ministers at the weekly cabinet meeting.He also referred to comments made by Abbas on Thursday in which the Palestinian leader pledged to hold those behind the kidnapping "accountable", and said there would be no new armed uprising against Israel. "His remarks will be tested not only by actions to return the boys home but by his willingness to dissolve the unity government with Hamas, which abducted the youths and calls for the destruction of Israel," he said.Meanwhile, the teenage son of an Israeli defence ministry contractor was killed on the Golan Sunday in the most serious incident on the plateau since the Syrian civil war erupted in 2011.Israel's defence ministry and the army said the 15-year-old was killed when a blast hit the car he was travelling in with his father and another contractor, both of whom were wounded.The boy, an Arab Israeli, was Mohammed Qaraqra from the northern village of Arabeh in the Galilee region, military radio said. The Israeli army called the explosion "an intentional attack" on a civilian vehicle by forces inside Syria, with a senior spokesman telling reporters Israeli tanks had fired at Syrian army posts in response.It was not clear whether there were any casualties on the Syrian side. "This is the most substantial incident on the border with Syria since the beginning of the civil war," said Lieutenant Colonel Peter Lerner, the army's foreign press spokesman, confirming it was the first death on the Israeli side.He said the shooting was deliberate. "This was an intentional attack, not errant fire," he said, adding that the target was a vehicle delivering water.