The group formerly known as the Islamic State of Iraq and the Levant says it is in full control of all of Syria's main oil and gas fields. The latest gains are further strengthening Islamic State's advance across eastern Syria, and reinforcing its stated goal of establishing a caliphate, or Islamic system of rule, straddling Syria and Iraq.
The Syrian Observatory for Human Rights said the group pushed out rivals Al Nusra Front from oilfields in Deir Az Zor province. Rebel groups in northern and eastern Syria have threatened to lay down their weapons unless they get reinforcements from exiled opposition leaders.
A statement released on behalf of those groups warned: 'Our popular revolution is today under threat because of the Islamic State.'
US president Barack Obama is proposing to commit half a billion dollars on training and equipping what the White House calls 'appropriately vetted elements of the moderate Syrian armed opposition.'
But is the real fight now against Syrian government forces or Islamic State fighters - who have eyes on a much bigger prize?
Presenter: Folly Bah Thibault
Isabel Nassief - research analyst at the Institute for the Study of War.
Abdullah Al Andalusi - political analyst and Islamic Affairs Specialist.
Shiraz Maher - senior research fellow at the International Centre for the Study of Radicalisation at Kings College London.