A dozen Taliban militants have been killed during a military operation in Afghanistan's southern province of Helmand, the country's defence ministry said on Saturday."Up to 12 armed insurgents were killed during a cleanup operation conducted by Afghan National Security Forces in Nad Ali and Marja districts of Helmand province over the past 24 hours," the ministry said in a statement, Xinhua reported.The security forces also found weapons and ammunition. They defused 30 roadside bombs and landmines in Helmand during the same period, the statement added.Helmand, notorious for poppy growing, is also a known Taliban stronghold.Afghan security forces have been clearing militants from restive provinces as the Taliban have been attempting to take territory and consolidate their positions ahead of winter in the mountainous Central Asian country.