The Islamic State of Iraq and the Levant (ISIL), which is battling to control a huge area of east Syria and western Iraq, has advanced along the Euphrates River in the oil producing Deir al-Zor province and driven back militants from al-Qaida's Nusra Front and other Islamic brigades.
The Syrian Observatory for Human Rights said the jihadist al-Qaida splinter group ISIL now controls most of the northeast bank of the Euphrates from close to the border with Turkey down to the town of Busayra nearly 200 miles (320 km) to the southeast.
A six-week offensive by the Islamic State in Iraq and the Levant (ISIL) against rival Islamists in eastern Syria has killed 600 fighters and driven 130,000 people from their homes, a monitoring group said on Tuesday.
A a larger six-month-old ISIL offensive against Syrian Kurds and other rebel groups has weakened the revolt against President Bashar al-Assad and killed thousands. According to the Syrian Observatory for Human Rights, the renegade group killed 15 Kurdish civilians, seven of them children, in an attack on a village in northern Syria,
It aims to extend that control all the way to the town of Albukamal on the Iraqi border, strengthening links between its Syrian and Iraqi wings, the Observatory's Rami Abdelrahman said.
Across the border, ISIL has made stunning gains, seizing control in most of Mosul, Iraq's second largest city on, Tuesday. The radical Islamist fighters succeeded in overrunning a military base and airport as well as freeing hundreds of prisoners in a spectacular strike against the Shi'ite-led Iraqi government.
The city's capture followed four days of fierce fighting in Mosul and other cities and towns in northern Iraq that has included a violent seizure of a university and bombings targeting civilians.
Now ISIL fighters have seized control of swathes of eastern territory close to the Iraqi border as the jihadi group is seeks to establish an Islamist state by connecting territory it controls in western Iraq and eastern Syria.
Territory in control of ISIL/REUTERS
The group follows al-Qaida's jihadist ideology but its leader Abu Bakr al-Baghdadi has defied orders by al Qaeda leader Ayman al-Zawahri to stop fighting in Syria and focus on Iraq.
Baghdadi fought first in Iraq before expanding into Syria when the 2011 uprising against President Bashar al-Assad was crushed by force and descended into civil war.
His enemies say ISIL has almost exclusively targeted rival rebels - including the Nusra Front which Baghdadi originally nurtured - rather than Assad's forces, as it exploits turmoil in Syria and insecurity in Iraq to carve out territory.