<P> According to one estimate, as of early 2008, 1,121 suicide bombers have blown themselves up in Iraq . Sunni suicide bombers have targeted not only thousands of civilians, but mosques, shrines, wedding and funeral processions, markets, hospitals, offices, and streets . Sunni insurgent organizations include Ansar al - Islam . Radical groups include Al - Tawhid Wal - Jihad, Jaish al - Ta'ifa al - Mansurah, Jeish Muhammad, and Black Banner Organization . </P> <P> Takfir motivation for many of these killings may come from Sunni insurgent leader Abu Musab al - Zarqawi . Before his death Zarqawi was one to quote Muhammad ibn Abd al - Wahhab, especially his infamous statement urging followers to kill the Shia of Iraq, and calling the Shias "snakes". An al - Qaeda - affiliated website posted a call for "a full - scale war on Shiites all over Iraq, whenever and wherever they are found ." Suicide bombers continue to attack Iraqi Shia civilians, and the Shia ulama have in response declared suicide bombing as haraam: </P> <P> حتی كسانی كه با انتحار می‌آيند و می‌زنند عده‌ای را می‌كشند ، آن هم به عنوان عملیات انتحاری ، این‌ها در قعر جهنم هستند Even those who kill people with suicide bombing, these shall meet the flames of hell . </P> <P> Some believe the war has strengthened the takfir thinking and may spread Sunni--Shia strife elsewhere . </P>

What is the problem between shia and sunni