U.S. Secretary of State Antony Blinken warned Tuesday that Washington would react “swiftly and decisively” if Iran or its proxy forces attack U.S. personnel after Tehran raised the risk of a larger Middle East conflict in recent days by unleashing the regional militias it has spent years arming.

For more than six months, these Iranian-backed militia groups refrained from launching drones or rockets against American troops in Iraq and Syria, as part of what appeared to be an undeclared truce between Tehran and Washington.