The U.S. military said Tuesday it has begun strikes against Iran after a U.S. Army Apache helicopter crashed off Oman near the Strait of Hormuz, AP reported.

U.S. Central Command described the action as a “proportional response to unjustified Iranian aggression.”

President Donald Trump blamed Iran for downing the helicopter and vowed retaliation, while Iran’s foreign minister warned foreign military forces near the country face constant risk.

The Apache went down near a key shipping route affected by the Iran-Israel conflict. In a first-of-its-kind operation, a U.S. drone boat rescued the helicopter’s two aviators after the crash.

Read more at AP.