Member of ISIS
Member of ISISReuters

The jihadist Islamic State of Iraq and Syria (ISIS) on Tuesday seized control of the key Syrian border town of Albu Kamal after a fierce three-day battle with rival fighters, AFP reported.

A spokesman for rebels fighting ISIS as well as President Bashar Al-Assad’s regime said the jihadists took the town after pouring in reinforcements from neighboring Iraq, where they have overrun chunks of territory in a swift offensive.

The takeover comes two days after ISIS declared a “caliphate” in territory they seized in both Syria and Iraq, and ordered the world’s Muslims to obey its leader Abu Bakr al-Baghdadi.

“The Islamic State took total control of Albu Kamal in (the oil-rich province of) Deir Ezzor, after fierce fighting pitting it against rebels backed by Al-Qaeda affiliate Al-Nusra Front,” said the Syrian Observatory for Human Rights, according to AFP.

Omar Abu Leyla, the rebel spokesman for Deir Ezzor province, told the news agency that “the battle was fierce... But ISIS has won this round.”

He said the jihadists won “after deploying major reinforcements from Iraq into Syria on Monday night.”

Fighting has raged for months in Deir Ezzor between ISIS jihadists and rebels backed by Al Qaeda's official branch in Syria, the Al-Nusra Front.

The fighting broke out after allegations that ISIS brutally abused civilians and other opposition fighters battling to topple the regime of Syrian President Bashar Al-Assad.

Tensions were further exacerbated when Al-Nusra and other rebel factions accused ISIS of killing Islamist Front commander Abu Khaled al-Suri in a suicide car bomb attack in February.

Meanwhile in Iraq, ISIS has seized a chemical weapons facility, Iraq's largest oil refinery, and become the "world's richest terrorist organization" by looting 500 billion Iraqi dinars ($425 million) from banks in Mosul.