BRUSSELS—European powers are likely to put off for weeks a decision on triggering a dispute procedure in the nuclear deal with Iran that could lead to international sanctions being reimposed, diplomats said, potentially further inflaming tensions with the U.S. over how to deal with Tehran.

Since July 1, Iran has deliberately breached two limits in the 2015 nuclear deal that placed tight restraints on Iran’s nuclear activities in exchange for the suspension of most international sanctions. Iran has threatened to take more as...