A US-backed force of Syrian Kurdish and Arab fighters has taken control of an Islamic State-held airbase west of the jihadist group's stronghold of Raqqa. The Syrian Democratic Forces (SDF) and a monitoring group said Tabqa airbase had fallen yesterday evening.<br/><br/>US helicopters airlifted hundreds of fighters behind IS lines at the start of the assault last Wednesday. The airbase's capture is seen as a significant step in the campaign to drive IS militants out of Raqqa.<br/><br/>The SDF is also aiming to seize the nearby town of Tabqa and the Tabqa dam, which the US-led multinational coalition has denied damaging in air strikes.