BEIRUT: Heavy clashes were underway Monday between several Syrian rebel factions and an Al-Qaeda breakaway group fighting for control of a border crossing with Iraq, opposition activists said, just hours after the jihadi group declared the establishment of a transnational Islamic caliphate.
The Britain-based Syrian Observatory for Human Rights said fighting between rebel groups and rivals in the Islamic State of Iraq and Greater Syria (ISIS) is concentrated in the town of Boukamal on the border between Syria and Iraq.
The jihadist group, which Sunday declared the establishment of an Islamic caliphate, controls much of northeastern Syria. In Iraq, it has recently captured cities and towns as well as border crossings, effectively erasing the frontier.
The group says that its Islamic state stretches from northern Syria to the Iraqi province of Diyala northeast of Baghdad, and has called on all Muslims worldwide to pledge allegiance to it.
Last week, beleaguered fighters of the Al-Qaeda-linked Nusra Front, which has previously fought the Islamic State in opposition-held territory in northern and eastern Syria, defected and joined the Islamic State in Boukamal, effectively handing over the border town to the powerful group, which controls the Iraqi side of the crossing.
Rebel infighting has turned into a war within a war in Syria, three years after the conflict began with largely peaceful protests against President Bashar Assad, whose family has ruled the country for more than four decades.
After the government brutally cracked down on the protest movement, many Syrians took up arms to fight back. As the uprising shifted into a civil war, the Western-backed Free Syrian Army emerged, a loose term for a collection of self-formed brigades and defectors from Assad's military that fight under a nationalist banner.
But Islamic fighters became the dominant force in the armed opposition, ranging from religious-minded Syrians calling for rule by Shariah law to more extreme Al-Qaeda-inspired fighters.
The Islamic State, which was at the time Iraq's Al-Qaeda branch, barged into the Syrian war in 2012, sending in its battle-hardened forces and recruiting foreign jihadis.
Other rebels initially welcomed the jihadis as allies against the Assad government, but soon turned on the group, accusing it of hijacking the uprising for its own transnational goals and imposing a brutal form of Islamic rule in the territories under its control.
Up to 7,000 people, the majority of them fighters, have been killed in the rebel-on-rebel violence across the opposition-held territory in the north since January, according to the Observatory's tally, which is compiled by its activists on the ground.