Screaming "kill, kill, kill," suicide bombers belonging to the Islamic State of Iraq, a militant organization connected to al Qaeda in Iraq, stormed a Chaldean church in Baghdad on Sunday. A spokesman for the group subsequently claimed they did so "to light the fuse of a campaign against Iraqi Christians." The assailants' more immediate grievance seems related to a demand that two Muslim women, allegedly held against their will in Egyptian Coptic monasteries, be released. When Iraqi government forces attempted to free approximately 120 parishioners who had been taken hostage, the terrorists -- who had already shot dead some of the churchgoers -- detonated their suicide vests and grenades, slaughtering at least half the congregation. But the massacre in Baghdad is only the most spectacular example of mounting discrimination and persecution of the native Christian communities of Iraq and Iran, which are now in the middle of a massive exodus unprecedented in modern times as they confront a rising tide of Islamic militancy and religious chauvinism sweeping the region. Christians are the largest non-Muslim religious minority in both Iraq and Iran, with roots in the Middle East that date back to the earliest days of the faith. Some follow the Apostolic Orthodox Armenian Church. Others subscribe to the 2,000-year-old Syriac tradition represented mainly by the Chaldean Catholic Church in Iraq and by Aramaic speakers widely known as Assyrians in both Iraq and Iran. Iraqi and Iranian Muslim leaders claim that religious minorities in their countries are protected. In September, former Iranian president Ayatollah Akbar Hashemi Rafsanjani reassured the patriarch of the Assyrian Church of the East that religious minorities are respected and safeguarded in Iran. Yet members of Iran's Christian denominations, like their Jewish, Zoroastrian, Mandean, and Baha'i counterparts, don't feel safe. A member of the National Council of Churches in Iran, Firouz Khandjani, lamented in August, "We are facing the worst persecution" in many decades, including loss of employment, homes, liberties, and lives, he said, "We fear losing everything." In Iraq, Chaldean and Assyrian Christian communities have witnessed increasing violence by militant Muslims against their neighborhoods, children, and religious sites since the U.S. invasion. Even pastors are not safe -- two died in the recent Baghdad bombing; many have been killed by Sunni and Shiite Iraqis since 2003. In Iran, other clergymen, including members of the Armenian, Protestant, and Catholic churches, have been arrested, kidnapped, imprisoned, tortured, or even summarily executed, over the past three decades. "Many Christians from Mosul have been systematically targeted and are no longer safe there," said Laurens Jolles, a UNHCR representative, in 2008, after Chaldean women were raped while their men, including Archbishop Paulos Faraj Rahho, were tortured and killed in warnings to Christians to abandon their homes and livelihoods. In Iran, Christian clerics have been targeted -- Tateos Mikaelian, senior pastor of St. John's Armenian Evangelical Church in Tehran was assassinated in 1994, as was Bishop Haik Hovsepian Mehr, who headed the evangelical Assemblies of God Church. Why Christians? Of the many justifications offered by al Qaeda and other fanatical groups in Iraq, and by hard-line mullahs in Iran, one is repeated most often: These indigenous Christians are surrogates for Western "crusaders." As early as 1970, Ayatollah Ruhollah Khomeini issued a fatwa accusing Christians in Iran of "working with American imperialists and oppressive rulers to distort the truths of Islam, lead Muslims astray, and convert our children." Fearing a backlash against their institutions and lives, Christians have often made efforts to prove their loyalty, as when Iranian Assyrians wrote to Supreme Leader Ayatollah Ali Khamenei in September denouncing American Christians who wished to burn Qurans as "enemies of God." But the roots of Christian decline in the Middle East actually date back centuries. In Iran, intolerance toward all non-Muslim minorities took a sharply negative turn from the 16th century onward with the forced Shiification of Iran by the Safavid dynasty. The early 20th century saw pogroms against Armenian, Assyrian, and Greek Christians in the Ottoman Empire and northwestern Iran. Under the Pahlavi shahs, Assyrians, Armenians, Jews, Zoroastrians, and Baha'is regained some of their rights and came to represent the modernizing elements of 20th century society. But the Islamic Revolution of 1979 undercut all those advances. Prejudice and oppression now occurs with impunity. The numbers speak for themselves: The population of non-Muslims in Iran has dropped by two-thirds or more since 1979. From Iran, these groups flee to Turkey and India -- often at risk to life and limb through the violence-ridden border regions of Iraq and Pakistan. The number of Assyrian Christians in Iran has dwindled from about 100,000 in the mid-1970s to approximately 15,000 today, even as the overall population of the country has swelled from 38 million to 72 million people over the same period. In Iraq, Christians are fleeing in droves. U.N. statistics indicate that 15 percent of all Iraqi refugees in Syria are of Christian background, although they represented only 3 percent of the population when U.S. troops entered in 2003. The U.N. High Commissioner for Refugees estimates that between 300,000 to 400,000 Christians have been forced out of Iraq since 2003. And Christians have left because the message from Sunni militants and Shiite ayatollahs is crystal clear: You have no future here. There is now an alarming possibility that there will be no significant Christian communities in Iraq or Iran by century's end. Christian schools, communal halls, historical sites, and churches are being appropriated by national and provincial governments, government-sponsored Muslim organizations, and radical Islamist groups. Economic and personal incentives are offered to those who adopt Islam. Last month, the Vatican convened a major summit to find ways of mitigating this crisis, noting that "Christians deserve to be recognized for their invaluable contributions ... their human rights should always be respected, including freedom of worship and freedom of religion." There is a faint glimmer of hope. On Aug. 5, the U.S. Senate adopted Resolution 322 expressing concern for religious minorities in Iraq. The quick, though unsuccessful, attempt by the Iraqi government this weekend to rescue the Christian hostages appears to have been in response to such American pressure -- no official Iraqi interventions had occurred in previous attacks. In Iran, however, the persecution of Christians continues unabated. Two Protestant pastors, arrested in post-presidential election crackdowns, face the death penalty. An Assyrian pastor was arrested and tortured in February 2010 and faces trial too. The Senate resolution noted that "threats against the smallest religious minorities

Eden Naby is a cultural historian of the Middle East. She has taught at the University of Wisconsin and Harvard University. Her book on Assyrian Christians will be published in 2011. Jamsheed K. Choksy is professor of Iranian and international studies at Indiana University and a member of the National Council on the Humanities.