Afghan police backed by the army have killed 51 militants in a series of operations across the conflict-ridden country since Saturday, the interior ministry announced on Sunday."Units of police have conducted several anti-terrorism joint operations with the national army and national directorate for security in Kunar, Nangarhar, Baghlan, Kunduz, Faryab, Badakhshan, Sar-e-Pul, Jowzjan, Kandahar, Zabul, Uruzgan, Logar, Ghazni, Paktiya, Herat and Badghis provinces over the past 24 hours during which 51 armed insurgents have been killed, 15 wounded and one was arrested," Xinhua quoted the ministry as saying in a statement.The statement didn't say if there were any casualties of security personnel.Taliban militants have stepped up terror activities in Afghanistan, launching their so-called annual spring offensive on April 24.