Foreign fighters are mostly Arabs from neighboring countries, who have entered Iraq, primarily through the porous desert borders of Syria and Saudi Arabia, to assist the Iraqi insurgency. Many of these fighters are Wahhabi fundamentalists who see Iraq as the new "field of jihad" in the battle against U.S. forces. It is generally believed that most are freelance fighters, but a few members of Al-Qaeda and the related group Ansar al-Islam are suspected of infiltrating into the Sunni areas of Iraq through the mountainous northeastern border with Iran. The United States and its allies point to Jordanian-born Al-Qaeda in Iraq leader Abu Musab al-Zarqawi as the key player in this group. Zarqawi was considered the head of an insurgent group called Al-Tawhid Wal-Jihad ("Monotheism and Holy War") until his death on 7 June 2006, which according to U.S. estimates numbers in the low hundreds.