Syria Rebels Will 'Lay down Arms' if No Aid to Fight IS

Rebels from northern and eastern Syria on Wednesday threatened to lay down their arms in a week if the country's exiled opposition does not help them fight the jihadist Islamic State (IS).

"We, the leaders of the brigades and battalions... give the National Coalition, the (opposition) interim government, the (rebel) Supreme Military Council and all the leading bodies of the Syrian revolution a week to send reinforcements and complete aid," the statement said.

"Should our call not be heard, we will lay down our weapons and pull out our fighters," it added.

The statement comes three days after IS declared the establishment of a "caliphate" straddling Syria and Iraq, referring to an Islamic system of rule that was abolished nearly 100 years ago

"Our popular revolution (against Syrian President Bashar Assad)... is today under threat because of the (Islamic State), especially after it announced a caliphate," said the statement.

The factions that signed the statement are local rebel groups based in Raqa, Deir Ezzor and parts of Aleppo province where fighting against IS has been most intense, and which are now under IS control.

IS first appeared in Syria's war in late spring 2013. It has since taken control of Raqa in northern Syria, much of Deir Ezzor in the east, and parts of Aleppo province.

Rebel groups from those areas have frequently complained of being poorly funded even though they are leading the fight against IS, formerly known as the Islamic State of Iraq and the Levant.

The statement comes days after U.S. President Barack Obama called on Congress to approve $500 million to train and equip the moderate Syrian opposition.

It also follows a visit late last week by Secretary of State John Kerry to Saudi Arabia, during which he said: "The moderate Syrian opposition... has the ability to be a very important player in pushing back against (the jihadists') presence."

Some Syrian rebels seeking Assad's ouster initially welcomed the war-hardened IS fighters among their ranks.

But their systematic abuses and quest for hegemony in opposition-held areas eventually turned the rebels against them and their project.

IS has kidnapped thousands of Syrians, many of them political activists and rebels, and carries out summary executions in areas under its control.

The group has been bolstered in recent weeks by an offensive it spearheaded in neighboring Iraq, capturing large swathes of territory as well as heavy weapons seized from fleeing Iraqi troops.

Syria's war began as a popular revolt demanding Assad's ouster, but morphed into a war after his regime unleashed a brutal crackdown against dissent.

Many months into the fighting, jihadists started to pour into Syria, and in January 2014, the country's rebels including Islamists launched a major offensive against IS.