The national unity agreement that was reached last month in Mecca has triggered a behind-the-scenes power struggle in Hamas, sources close to the Islamic movement in the Gaza Strip revealed Tuesday. Meanwhile, fierce fighting erupted Tuesday evening between Hamas members and gunmen belonging to a large clan in Gaza City, Palestinian security officials reported. The clashes began after a car carrying several Hamas members was fire upon in the Zeitoun neighborhood, they said, adding that Ala Hadad, a senior Hamas operative, was killed and four others injured. "Hamas is facing a serious split," the sources said. "Opposition in Hamas to the Mecca agreement is growing as some of the movement's senior officials are talking about a possible revolt." The "rejectionist" camp in Hamas, led by Interior Minister Said Siam and Foreign Affairs Minister Mahmoud a-Zahar, is opposed to the Mecca agreement under the pretext that Hamas made too many concessions to Palestinian Authority Chairman Mahmoud Abbas's Fatah faction. Both Siam and Zahar have privately criticized Prime Minister Ismail Haniyeh and Syria-based Hamas leader Khaled Mashaal for signing the agreement, a top Hamas official in Gaza City told The Jerusalem Post. He said the two, along with a number of senior Hamas figures in the Gaza Strip, have refused to participate in coalition talks with Fatah representatives over the past few weeks. The two are expected to lose their jobs in the new Hamas-led coalition. "Siam and Zahar are unhappy with the agreement not only because they won't serve in the unity government, but because they believe that Hamas has made far-reaching political concessions," the official said. "They are convinced that Hamas is gradually abandoning its ideology as Fatah did when it signed the Oslo Accords with Israel more than a decade ago." Although Siam and Zahar have thus far refrained from public criticism of the Mecca agreement, the two are said to be quietly campaigning against the accord. Siam, for instance, has made it clear that he and his supporters will resist any attempt to dismantle Hamas's Executive Force that he established in the Gaza Strip last year. Zahar, on the other hand, is said to have warned that Hamas was headed toward a serious crisis because of its agreement to sit with Fatah in the same coalition. Siam and another prominent Hamas figure, Sami Abu Zuhri, were recently summoned to Damascus for emergency talks with Mashaal, who reportedly reprimanded them for campaigning against the Mecca agreement. The tensions among the political leaders of Hamas have have also hit the movement's field activists. Hamas's two main militias, the Executive Force and Izzadin al-Kassam, are also facing divisions over the Mecca agreement. Leaders of the two groups have warned the Hamas leadership against falling into what they consider "a trap" by Abbas and the US. Some Hamas preachers have also joined the "rejectionist" camp by speaking out in the mosques against the deal with Fatah. The rejectionists cited a number of "changes" in Hamas's traditional policy as evidence that the movement was on the verge of betraying its ideology. These include: Hamas's readiness to accept a temporary state in the West Bank, Gaza Strip and east Jerusalem; its readiness to abandon the armed struggle by accepting a long-term truce with Israel; its readiness to remain committed to the current cease-fire with Israel in the Gaza Strip; its readiness to endorse the Saudi peace initiative from 2002 and Haniyeh's announcement that he will attend the upcoming Arab summit in Riyadh later this month and Mashaal's reported promise to the Russians to work toward halting rocket attacks on Israel from the Gaza Strip. In an attempt to calm the fears of the Hamas rebels, some of the movement's top officials have issued a number of statements clarifying their strategy in the aftermath of the Mecca agreement. "The agreement does not mean that Hamas will recognize the Israeli entity," said Hamas spokesman Ismail Radwan. "The resistance will continue," declared Osama Hamdan, Hamas's representative in Lebanon. "Hamas continues to regard the resistance as a strategic option, and there is no room for concessions in this regard." A senior Fatah official said "it was obvious" that some Hamas leaders and activists were working towards "derailing" the Mecca agreement. "The divisions in Hamas will deepen after the formation of the unity government," he predicted. "This is perhaps one of the biggest achievements of the agreement."