Seizing the city would give rebels control of an entire province of Syria for the first time in the 23-month conflict, but it will also add a volatile new element to the war.
The province of Deir al-Zor borders on Iraq, and the rebels sieging the city include radical Sunni fighters from Jabhat al-Nusra — which is led by veterans of a l-Qaeda in Iraq (AQI).
Nusra members — the opposition's best frontline fighters — already control wheat silos, a textile factory, and oil fields across Deir al-Zor, and the 10,000-strong force would think little of the border between Syria and Iraq as it attempts to create a seventh-century style Islamic Caliphate.
From 2004 to 11 AQI fought a brutal guerrilla war against the Iraqi government and the U.S. military with the help of a deep support network of fixers, safe houses, financiers, and radical religious figures in Syria.
By 2009 U.S. intelligence officials became concerned that e astern Syria was becoming a new al-Qaeda haven.
It now appears to be a hotbed as t he Syrian civil war has reversed the networks — AQI now contributes money, weapons, expertise, and veteran fighters to al-Nusra.
"The Sunnis in Anbar are helping with weapons and ammunition," the leader of the powerful Al-Qadisiyah Brigade told Reuters . "Their days (of fighting) will come soon and Inshallah (God willing) we will go to jihad with them. Those Sunnis are our brothers."
Given the resurgence of Islamic State of Iraq (ISI) — another AQI offshoot — and the group's recent call on Sunnis to rise up against the Shiite-led Iraqi government, the fall of Deir al-Zor may be an ominous sign of an emerging, transnational sectarian conflict.
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