Pakistani forces have secured several key areas in the Taliban-held main town of the Swat valley as they battle to gain control of the capital of the northwestern district, officials said Sunday. The ground assault on Mingora, a city with an estimated population of about 300,000 many of whom have fled marks the most crucial part of the military's blistering offensive against the Taliban in the scenic valley. Officials said they had taken control of several important intersections and three squares in Mingora, including the notorious Green Square where the Islamist extremists reportedly carried out beheadings late last year. "Security forces are engaged in clearing landmines. They are also conducting search operations in the areas under their control," a security official said on condition of anonymity, as he was not authorised to speak to the media. Another military official said that street battles were still raging in Mingora, where Taliban insurgents have in recent weeks been patrolling with guns and rocket launchers, according to terrified residents. "Clashes are going on between security forces and militants in Nawa Kilay neighbourhood of Mingora and its western suburb of Qambar," he said. A curfew remained in place in the city and gunfire could be heard, the official said, but there was no shelling overnight. Mingora has effectively been under Taliban control for weeks and -- as the administrative and business hub of the entire district -- its capture is essential for the military to be able to declare victory in Swat. Pakistan says up to 15,000 troops are taking on 4,000 well-armed militants in Swat, where Islamabad late last month ordered a battle to eradicate fighters who advanced to within 100 kilometres (60 miles) of Islamabad. Chief military spokesman Major General Athar Abbas said Saturday that parts of Mingora had already been cleared and that 17 militants, including an important commander, were killed.