Security forces killed 17 militants in various operations in Afghanistan, authorities said Friday, as US President Barack Obama was due to announce a new strategy to battle extremists in the region. The clashes on Thursday were all in southern Afghanistan, a Taliban stronghold that will be the focus of 17,000 extra US troops due to begin deploying to Afghanistan late spring in a new focus on the troubled country. The US military said that troops working with Afghan forces killed 11 militants in a firefight in Helmand province late Thursday. The battle was during a raid "to stop a key Taliban insurgent and disrupt a cell responsible for roadside bomb-making and emplacement in northern Helmand province," it said. The insurgent and his associates were killed. Such bombs are the main Taliban weapon in an insurgency that last year reached its deadliest since the hardline Islamists were removed from government by the late 2001 US-led invasion.