Gaza's Hamas rulers on Sunday ordered census workers to halt the first Palestinian population count in a decade, derailing a rare joint endeavor with the rival Fatah movement. Hamas had agreed to cooperate with the census, which is being conducted by Palestinian Authority President Mahmoud Abbas's rival government in the West Bank. But Hamas officials on Sunday shut down the Gaza census office, saying the surveyors had violated an agreement to share their data with Hamas. "Data can't just be given to one side and not the other," said Mohammed Madhoun, an official in Gaza's Hamas government. "The government wants to make use of it for its future projects." Demographics play a central role in the Israeli-Palestinian conflict. Jews are a solid majority inside Israel, comprising roughly 80 percent of the population of 7 million. However, if the estimated 3.9 million Palestinians in the West Bank and Gaza are added to the roughly 1.7 million Arab citizens of Israel, Arabs make up nearly half the population. Many Israeli demographers believe that the Arab population could soon exceed the Jewish population. To ensure that Israel can maintain its character as a democracy with a solid Jewish majority, Prime Minister Ehud Olmert supports a withdrawal from much of the West Bank and parts of east Jerusalem, following Israel's pullout from Gaza in 2005. Last week, he said Israel could one day face a struggle resembling apartheid-era South Africa if it doesn't reach a peace agreement with the Palestinians. Palestinians had said they hoped the first census since 1997 would help them in future peace talks with Israel. The census at first had escaped the rivalry between Hamas and Fatah because of their common interest in the count. Two earlier phases, collecting data on institutions and residences, were completed without interruption on Nov. 15. The final stage, counting people, began Saturday in the West Bank, but not in Gaza, and is expected to take two weeks. Hamas radio and mosques even called for people to cooperate with the surveyors. Hamas did not ask for information gathered in earlier stages of the census, and it wasn't immediately clear why the group was suddenly demanding the data. Hamas took control of Gaza by force in June, prompting Abbas to expel the Islamic group from the Palestinian government and install his own Cabinet in the West Bank. There has been little contact between them since then. Loai Shabana, head of the Palestinian Central Bureau of Statistics, accused Hamas of ruining what was meant to be an apolitical effort. "This is blatant and unjustified interference that sabotages a professional endeavor," Shabana, who is appointed by the president, said from his West Bank office. He added that the data is off limits to all political factions until it is complete. "No lawmaker or government official can get a peak at our records. This would...undermine our credibility," he said. "I wish they let national interest prevail, and not let temporary problems between Hamas and Fatah ruin a strategic project." The census will cost $8.6 million (â‚¬5.8 million), with the Palestinian Authority paying 20 percent. The rest comes from the United Nations, Saudi Arabia, the Swiss Agency for Development and Cooperation, the Netherlands and the Organization of Petroleum Exporting Countries. Some 5,000 Palestinians were working on the project, including 2,000 in Gaza.