The arrest this week of the "Zeitoun terror cell" is a significant moment in the ongoing battle between the Egyptian security forces and homegrown Islamist extremism. The cell, we are told, plotted to assassinate the Israeli ambassador to Egypt, Shalom Cohen. It is also thought to have been involved in a series of acts of terror in Egypt earlier this year. The uncovering of the Zeitoun cell points to a revival of domestic Sunni Islamist terrorism in Egypt. Parallel to this, though separate from it, recent months have also seen the unearthing of a Hizbullah network active in Egypt. It is important to keep in mind the major differences in orientation between these two trends of Islamism. The emerging picture, however, also points to significant aspects of commonality between the two structures. The Zeitoun cell emerged from the domestic Egyptian extreme Sunni Islamist scene. A series of actions associated with this trend have taken place in recent months. A French tourist was killed in a bomb explosion at Cairo's Al-Azhar/Khan el-Khalili in March. The Saint Virgin's Coptic Church in the Zeitoun district was bombed on May 12. These acts bear the typical hallmarks of activity of Egyptian Sunni extremists - namely, anti-Christian sectarianism, hostility to the presence of tourists in Egypt and the belief that the possessions of non-Muslims may be taken at will. The members of the cell have admitted to being in communication with representatives of the al-Qaida network abroad. Their intention was to reassemble in Saudi Arabia after undertaking actions in Egypt, and from there to join the Sunni insurgency in Iraq. As is often the case with groups claiming association with al-Qaida, the real capabilities of the Zeitoun cell are not clear. Its members said in court that their plan for the assassination of the Israeli ambassador had been ongoing since 2007. They also admitted that the tight security around the embassy had prevented it from being put into operation. It should be borne in mind, in order to avoid the confusion found in the statements of some Israeli spokesmen in the last days, that it is this Egyptian Sunni group which is suspected of planning to kill Ambassador Cohen. Parallel to this, a Hizbullah-led structure has also been revealed in Egypt in recent months. In April, Egypt announced the arrest of 49 people said to be involved with a network led by Hizbullah member Mohammed Mansour and personally sanctioned by movement General-Secretary Hassan Nasrallah. This structure was accused of preparing to commit crimes against Egypt." This included "observing the movement of ships in the Suez Canal, and the tourist villages in the northern and southern Sinai Peninsula, in order to attack them, providing Hamas in Gaza with arms and money," and "spreading Shi'ite ideas in Egypt and inciting the Egyptians against their government." The Salafi trend in Sunni Islam of which al-Qaida forms a part is violently opposed to the Shi'ite Islam of Hizbullah and Iran. Nor is this opposition purely theoretical. Iraq teetered on the verge of sectarian civil war between Sunni and Shi'ite three years ago, and such a conflict may yet emerge. The Sunni insurgency that the members of the Zeitoun cell hoped to join is as much opposed to the Iraqi Shi'ites as it is to the US. Indeed, the key strategic fault line in the region today pits Shi'ite Iran and its allies against the traditionally dominant Sunni powers of Egypt and Saudi Arabia. Egyptian and Saudi fear of Iran is what is driving the behind the scenes cooperation of these countries with Israel. But the genuine nature of the Sunni-Shi'ite split notwithstanding, it is worth noticing that both the Zeitoun cell and the Hizbullah network led by Mohammed Mansour sought to make war against Israel. That is, there is one issue, and probably one issue alone, which can trump the split between Sunni and Shi'ite, and it is the joint enmity toward the Jews and Israel. Shi'ite Iran knows this very well, which is precisely why it seeks to launch a bid for the "ownership" of the Palestinian issue. The only real inroads in the Arab world beyond the Shi'ites which Iran has made have all been in connection with its proxy war with Israel. Mansour's network, we are told, included Sudanese, Palestinians and Egyptians. Even more significantly, two members of the Muslim Brotherhood have been accused of association with it. "Our enemy and Hizbullah's enemy is the same," as Brotherhood parliamentary leader Hussein Ibrahim recently put it, in explaining his movement's attitude toward the Lebanese Shi'ite group. All of which goes to prove that while it is crucial in analytical terms to be clear as to who precisely is responsible for what, the details should not be allowed to obscure the relative clarity of the larger picture. Israel is the single largest contributor to Islamic ecumenicalism in the Middle East. Sunni and Shi'ite Islamists, at least for a while, can bury their differences in the service of the common hatred. Jonathan Spyer is a senior researcher at the Global Research in International Affairs Center, IDC, Herzliya.