Islamic State militants claimed responsibility Thursday for a pair of bombings that killed dozens of people a day earlier in the largest attack in Iran since the country’s 1979 Islamic Revolution, dispelling suspicions that Israel might have been behind the attack amid worries of a broadening regional conflagration.

The blasts took place with the Middle East on edge because of the war in Gaza between Israel and Hamas—an Islamist militant group that has moved closer to Iran in recent years—and increasing tensions between the U.S. and Israel on one side and other Iranian-backed militant groups in Lebanon, Syria, Iraq and Yemen on the other.