In April this year, Pakistan’s interior ministry announced a revision to its list of proscribed organizations, adding the Iranian-backed Zainabiyoun Brigade. Made up of  Pakistani Shiite Muslims, the armed group is not exactly a novel actor. It has been operating in Syria for more than a decade, and Pakistan’s law enforcement institutions have long kept an eye on its recruitment drives—and at times also arrested its members. However, up until April, the outfit had evaded a total ban.

The motives behind the proscription appear to be a mix of internal and external factors. Given Zainabiyoun’s close ties with Iran, Islamabad has assessed that the move will likely impact the relationship with Tehran. To balance the...