New Delhi, March 18 -- Even as the US-Israel war on Iran has put the world on edge, another flare-up closer home is threatening regional stability. As Kabul has reported, at least 400 people were killed in an airstrike by Pakistan that struck a hospital in Afghanistan.

While Islamabad denied that its forces struck a civilian target, the attack has sent out shockwaves, inviting criticism from New Delhi, which described it as a "massacre dressed as a military operation."

Killing civilians violates the conventions of warfare. Pakistan had hinted at regime change in Kabul before it deployed force in a campaign whose stated goal was to eliminate a cross-border threat of terror. But war plans rarely survive contact with reality, so this looks...