Sunni militants led by the Islamic State of Iraq and the Levant (ISIL) took control of an Iraq-Syria border crossing after Syrian rebels withdrew overnight, security officers and witnesses said.

The sources said insurgents took control of the Al-Qaim border crossing, one of three official border points between Iraq and Syria, after gunmen linked to the Free Syrian Army (FSA) and Al-Qaeda-affiliated Al-Nusra Front left.

ISIL, which grew from the ranks of Al-Qaeda before splitting with the global terror network, is active in both Syria and neighboring Iraq and seeks to set up an Islamic state that straddles both countries.

“Gunmen took full control of Al-Qaim and areas surrounding it,” a police lieutenant colonel said, speaking on condition of anonymity.

He said the militants, who include ISIL but also several other armed Sunni groups, did not enter the actual border crossing buildings for fear of booby traps.

An army major confirmed that the town and its surrounding areas were in insurgent hands.

The takeover of Al-Qaim spurred families in the town to flee, according to an Iraqi border guard whose unit is stationed in the town of Rawa, to the east.

Gunmen loyal to the FSA and Al-Nusra Front seized the Iraqi side of the border crossing on June 17 following the withdrawal of security forces and after having already held control of the Syrian side.

A broad militant alliance including ISIL and other groups has overrun a swathe of territory north of Baghdad in less than two weeks, alarming the international community and threatening Iraq’s very existence.

ISIL has been battling Iraqi government forces since June 9, when in launched the lightening offensive.

After performing poorly during the initial period of the onslaught, the Iraqi security forces appear to have recovered and are fighting to retake territory, with mixed results.

On Friday, Jihadists from ISIL executed three officers of the Free Syrian Army, a monitor said Saturday.

The bullet-riddled bodies of the three were found on Friday, two days after suspected Islamist militants kidnapped them in the oil-rich eastern province of Deir Ezzor, said the Syrian Observatory for Human Rights.

The radical group has faced a major backlash from other rebels fighting to topple the Syrian regime and from Nusra Front amid accusations of atrocities in Syria’s three-year war.

The FSA this month called for help from “friendly and brotherly Arab nations” to fight ISIL in Deir Ezzor.

Rebels in Syria, including Al-Nusra Front militants, have been battling ISIL since the start of the year, in fighting that has reportedly killed more than 6,000 people.

The clashes have mostly raged in the north and east of the country, and on Friday ISIL seized control of the areas of Hafez and Muhassen in Deir Ezzor.

The FSA officers executed by the jihadists had been kidnapped in Hafez, the Britain-based Observatory said.