BEIRUT, June 25 (Reuters) - Syria's al Qaeda wing has pledged allegiance to rival group the Islamic State in Iraq and the Levant (ISIL) in a Syrian border town, a monitoring group said, strengthening ISIL's control of both sides of the Syria-Iraq frontier.
Fighters from Nusra Front, the Syrian wing of al Qaeda, took an oath of loyalty to ISIL in the town of Albu Kamal, close to the Iraqi border, the British-based Syrian Observatory for Human Rights and an Islamist website said on Wednesday.
The central leadership of al Qaeda has disowned ISIL and proclaimed the Nusra Front as its official Syrian affiliate.
ISIL, which seized Iraq's main northern city Mosul on June 10, has since marched virtually unopposed towards Baghdad and is in control of major border posts on the frontier with Syria.
The group also controls large parts of eastern Syria, where it has both clashed with rival rebels groups and occasionally fought alongside them, complicating the three-year-old insurgncy against President Bashar al-Assad.
Twitter users posted a photo they said showed the Nusra Front leader of Albu Kamal, Abu Yusuf al-Masri, swearing loyalty to one of ISIL's prominent fighters.
"It is very important because Nusra is strong in Albu Kamal," the Observatory's Rami Abdurrahman said.
"We cannot say (ISIL) controls Albu Kamal but we can say they are now in Albu Kamal." (Reporting by Sylvia Westall; Editing by John Stonestreet)