Abstract. The article explores the religious expansion of the Islamic Republic of Iran in the Arab countries of the Middle East. Socio–political precipitants and motives of Iran’s religious policy in the region are addressed through the prism of the Syria crisis. Special attention is paid to a shifting paradigm of armed conflicts in the region as a factor influencing the rise of paramilitary forces (militia) and the choice of instruments of Iran’s humanitarian policy in Syria and Iraq. The history of various Shia militias in Syria and Iraq, their ideological basis and results of their activities are examined. On the basis of comparative analysis, an author’s typology of such groups is proposed. Active spread of the Shia doctrine, the formation of Shia–majority governments, support for non-state groups, and the creation of pro-Iranian militias are explored as strategic guidelines for Iran’s religious expansion in the Middle East. On the one hand, it is concluded that the integration of Shia militias in regular Arab armies along with the spread of the Shia doctrine rooted Iran in Arab social fabric and strengthened its political and military positions in the Middle East. On the other hand, it is shown that Iran’s sectarian policy affected Tehran's relations with key regional, international players in the region in more ways than one. Despite Tehran’s political statements and preferences, Shia militias’ attacks on the U.S. and Israeli targets in the region de facto have made Iran a part in Gaza war and have also affected its rapprochement with the Arab states and its cooperation with international partners in the process of reconciliation in Syria. In view of the significance of the Palestinian–Israeli conflict for Russia’s Middle East policy, the article contributes to the study of the Iranian policy in the region and sheds the light on Iran’s behavioral model in crisis conditions in the Middle East.