KABUL, Afghanistan — A day after a lethal Taliban assault on an army base in northern Afghanistan, an official said on Saturday that at least 140 soldiers had been killed, making it the single deadliest known attack on an Afghan military base in the course of the long war. “Today, there was even a shortage of coffins,” said the official, Ibrahim Khairandish, a member of the provincial council in Balkh Province, where the attack occurred. Citing information from army officials, Mr. Khairandish said 60 soldiers had also been wounded in the attack. The soldiers, most of them unarmed, were shot...