BEIRUT - Hezbollah has captured much of an Islamic State pocket on Syria's side of the border with Lebanon in a joint offensive with the Syrian army, its leader said on Thursday.In parallel with the fighting, talks on a truce have begun with Islamic State but a military victory is more likely, Sayyed Hassan Nasrallah said in a televised speech.Iran-backed Shi'ite Hezbollah and Syrian troops have been fighting to oust Islamic State militants from Syria's western Qalamoun region.The attack began last week, coinciding with a Lebanese army offensive against Islamic State on its side of the border near the town of Ras Baalbek in northeast Lebanon.The zone straddling the border is the last part of the Lebanese-Syrian frontier under the militants' control.Both offensives have advanced towards the Syrian-Lebanese border from opposite sides. The Lebanese army says it is not coordinating the assault with Hezbollah or the Syrian army."So far, more than 270 square km have been fully captured on Syrian land (by Hezbollah and the Syrian army). Around 40 square km remain under Daesh control," Nasrallah said. The frontier battle was nearing a "very big victory," he added. Northeast Lebanon saw one of the worst spillovers of Syria's war into Lebanon in 2014, when Islamic State and Nusra Front militants briefly overran the border town of Arsal.The fate of nine Lebanese soldiers that Islamic State took captive then remains unknown."The first condition of any deal reached with Daesh will be revealing the fate of the Lebanese soldiers and returning them to their families," Nasrallah said on Thursday.Hezbollah has played a major role in fighting Sunni militants along the border during the six-year Syrian war, and has sent thousands of fighters into Syria in support of President Bashar al-Assad's government.