(CNN) -- The extremist Sunni militant group that recently declared a caliphate in parts of Syria and Iraq wrested control of a major Syrian oil field in a sweeping land grab Thursday, a UK-based monitoring group said. A string of villages and towns along the Euphrates River fell like dominoes to the Islamic State in Iraq and Syria, bridging the Syrian province of Deir Ezzour with the group's recently gained territories in Iraq's Sunni heartland, the Syrian Observatory for Human Rights (SOHR) reported. A video statement from the leaders in the town of al-Shahil announcing their withdrawal from all anti-ISIS organizations triggered the quick fall of a majority of Deir Ezzour province.
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Oil field had been in hands of al Qaeda affiliate Nusra Front
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Field can produce 75,000 barrels of oil daily
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ISIS declared caliphate in parts of Syria and Iraq over the weekend
They just fled," a bearded radical fighter from @placeholder said in amateur video posted online Thursday from the oil field, "as proof, here is their ammunition and weapons."