Following a week of near-daily Palestinian violations of the Israeli-Hamas cease-fire, senior defense officials said Thursday that the truce could be in its final stages and that as a result the IDF was preparing for possible future incursions into the Gaza Strip. "It is not clear how much longer the cease-fire will last and we need to be prepared for an operation in Gaza," a senior defense official told The Jerusalem Post shortly after two Kassam rockets struck the western Negev Thursday afternoon. Both rockets both hit in open areas, causing no casualties or damage. A faction of Fatah's Al-Aksa Martyrs Brigades claimed responsibility for the attack. On Thursday evening Hamas said it had arrested the two men who had fired the rockets, according to an official from the Fatah-affiliated Al-Aksa Martyrs Brigades. Reuters quoted the official as saying that Hamas's security forces had detained two of its members who were part of a Kassam launching squad. "They chased the two after they fired the rockets and captured them," he said. A senior Hamas leader confirmed on Thursday that his group will hold to the cease-fire and stop violators. The remarks by Moussa Abu Marzouk came after two days of talks with Egypt's chief of intelligence, Omar Suleiman, who is the main mediator in the fragile truce that started June 19. In a statement before returning to Syria, Abu Marzouk called for "solidifying" the truce, saying it was in the Palestinians' interest. He also promised that his group, which controls the Gaza Strip, will stop violators who have been firing rockets into southern Israel. Al-Aksa had said earlier that an 18-year-old Palestinian who was shot and killed by IDF troops Thursday morning, after crossing the Gaza fence into Israel, belonged to its ranks. The troops called on the youth to stop and after he tried to flee, they opened fire fearing a terror infiltration. An inspection of his body revealed that he was unarmed. It was the first death on either side since the Egyptian-mediated cease-fire went into effect on June 19. "We will not let this crime pass silently," the group had said in a text message to reporters. It did not say what the young man was doing along the border. Hamas said it considered the predawn shooting of the 18-year-old a violation of the truce. "The Palestinian factions show a great commitment to making this understanding successful, but the occupation must also be committed to their obligations," Hamas spokesman Sami Abu Zuhri said. Late Wednesday night, a Palestinian gunmen affiliated with Fatah was killed during an arrest raid in Jenin. Also Thursday, eight Palestinians from the Isawiya in southeast Jerusalem were arrested on suspicion of throwing Molotov cocktails at cars on the road to Ma'aleh Adumim and near the Mount Scopus campus of the capital's Hebrew University, authorities announced Thursday. The eight were members of a cell of the Popular Front for the Liberation of Palestine. In other violence, a border policeman was lightly wounded by a rock thrown by anti-security barrier demonstrators in the West Bank town of Na'alin, north of Modi'in. Hundreds of Palestinians and Israeli protesters clashed with police and several of the demonstrators were also reportedly hurt. The army said they were demonstrating in a closed military zone and that security forces were trying to disperse them using crowd control measures. Dozens of IDF jeeps and trucks entered Nablus before dawn Thursday, and soldiers raided a medical clinic, confiscating computers and documents, witnesses said. Some of the offices were ordered closed, and soldiers also confiscated five schoolbuses, they said. The IDF confirmed an operation against Hamas in Nablus, but offered no details. Palestinian Authority Interior Minister Abdel Razek Yehiyeh said the Israeli raids were undermining the Palestinian government's efforts to establish law and order in the West Bank. "We condemn these practices and see them as sabotaging our security achievements," he told a news conference in Ramallah. AP contributed to this report.