The latest skirmish was the fiercest yet.

Pakistan's ceasefire agreement with the Afghan Taliban hinges on their ability to rein in militant attacks on Islamabad from their soil, Defence Minister Khawaja Muhammad Asif told Reuters on Monday.

“It has been decided that neither country will undertake any hostile actions against the other, nor will they support groups carrying out attacks against the Government of Pakistan,” Zabihullah Mujah...