At least 20 militants have been killed when Afghan and Nato forces called in air support after coming under attack from a large number of insurgents in northern Afghanistan. Nato's International Security Assistance Force (ISAF) today said the warplanes were scrambled when combined forces patrolling in the northern province of Baghlan last evening were attacked by rockets and machine-gun fire. <br/><br/>Afghan army General Murad Ali Murad confirmed the incident and said it occurred along the Kabul-Kunduz Highway, a key supply route for the international forces.The clash came as Afghan leaders and their international backers were set to hold a major conference in London later today to chart the future of operations in the strife-torn nation.