* Town was one of last in western Aleppo held by government
* Rebel video shows tanks withdrawing
BEIRUT, July 22 (Reuters) - Syrian rebels seized the northern town of Khan al-Assal on Monday, activists said, one of the last towns in the western part of Aleppo province that was held by President Bashar al-Assad's forces.
An army build-up around the province in order to retake Aleppo city has been dogged by rebel counter-attacks, although a string of government victories elsewhere in Syria has shifted the battlefield tide in Assad's favour after more than two years of bloodshed.
The Syrian Observatory for Human Rights, an anti-Assad monitoring group, said army officers surrendered the town on Monday morning after rebels surrounded a southern district.
Video footage posted on the Internet by rebel groups showed army tanks withdrawing from the town. Another video showed a dead commander who rebels said led the government resistance in the town, which has been besieged for weeks.
Aleppo is part of a crescent of regions in northern Syria that have become a stronghold for rebels fighting to end four decades of rule by the Assad family.
Insurgents have been blockading government-held areas in Aleppo city, Syria's largest urban centre and once its commercial hub. Aleppo has been mired in a bloody stalemate since rebels launched an offensive in the province last year.
Assad's forces have responded to the rebel advance on Khan al-Assal with a string of air raids in the area.
The Observatory says more than 100,000 people have been killed in Syria's insurgency, which grew out of street protests in the southern town of Deraa in March 2011. Millions of people have been displaced and ancient buildings and artefacts have been destroyed across the major Arab state. (Reporting by Oliver Holmes and Reuters TV in Beirut; Editing by Alison Williams)
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