Many Shia militias claim simply to be defending Shia holy sites. In his office in the Baghdad district of Karrada, Mr Khafaji claims his men in Syria are not fighting for Mr Assad. But the militias’ role goes far beyond the shrines. Hizbullah people make no bones about controlling southern Syria, on the Israeli border. They hint that the land will not be given back to Mr Assad. A Hizbullah commander says that in Syria Hizbullah calls the shots. “Each country is a separate operation, but the goal is one,” says a commander of a militia brigade in Syria. Mr Khafaji hopes eventually for “a Guards of the Shia Revolution, one force across the whole region.” 
That may be fanciful. Hizbullah fighters are contemptuous of their Shia comrades elsewhere. “Hizbullah follows the Koran; our men have a role, tactics and a plan,” says the brigade commander. He calls some Iraqi militias “extremists” and criticises their brutality.
Distrust between Shia militias and some of their allies is rife, partly because of sectarian differences. Hizbullah says that, in some cases, Mr Assad’s Sunni pilots have bombed the positions of their Shia allies. Western governments have generally viewed Shia militias as less of a worry than their Sunni counterparts, though they are often as bloody. One reason is that they do not yet target Westerners. Nonetheless, Shia militias are exacerbating violence across the region. Though Iran does also back some non-Shia or mixed groups, including the Iraqi Kurds, Palestine’s Hamas and the NDF, its actions are generally becoming more sectarian.
The ubiquity of Iranian proxies across the Middle East places America in an awkward position. In Iraq, its air strikes are supporting the Shia militias fighting in Tikrit. In Yemen, though, America is offering logistical and intelligence support to Saudi-led forces against Shia Houthis.
Iran and its proxies risk spreading themselves too thin. Sunnis outnumber Shias by nine to one. Disgruntlement is rising, and not just among Sunnis. On March 13th Ayatollah Ali al-Sistani, Iraq’s leading Shia cleric, warned Iran not to forget that Iraq is an independent state.

https://twitter.com/miirwais/status/625018303765970944 
July 23, 2015: Iran accused of sending Afghan Prisoners to Syrian war. So far, 700 Afghan Hazaras have been killd fighting for Assad