As the G7 summit approaches, South Korea faces difficult decisions regarding its potential contribution to securing the Strait of Hormuz.

The expected reopening of the Strait of Hormuz under a US-Iran ceasefire framework could ease pressure on South Korea’s energy-dependent economy while creating a thornier diplomatic problem for Seoul: how much should it contribute to securing the waterway? That question is likely to shadow President Lee Jae Myung’s visit to the Group of Seven summit this week in Evian-les-Bains, France, where the wars in Ukraine and Iran are expected to dominate talks among G7 leaders and several invited...