The U.S. military said Tuesday that it carried out strikes on Iran following the crash of an Army helicopter near the Strait of Hormuz that President Donald Trump blamed on the Islamic Republic.

U.S. Central Command said on social media that the strikes would be “a proportional response to unjustified Iranian aggression.” Iranian state media reported that explosions were heard on Qeshm Island in the Strait of Hormuz, a critical shipping lane that Iran has effectively closed during the war, before saying that the wave of American attacks in the south has “subsided.”

Trump said earlier in a social media post that Iran had shot down the aircraft while it was on patrol over the strait and declared that the U.S. “must, of necessity, respond to this attack.” Iran’s top diplomat said foreign military forces near the country’s territory “are at constant risk” and later said after the strikes that Iran “will leave no attack or threat unanswered.”

The downing of the helicopter and the resulting strikes by the U.S. military further strained a two-month ceasefire a day after Iran and Israel exchanged fire for the first time since the fragile truce took effect. Iranian state television said Tuesday that the Israeli attacks killed at least two members of the country’s air-defence units.

Since the U.S. and Israel began striking Iran on Feb. 28, the war has shaken the global economy, driven up energy prices around the world and made many basics, including food, more expensive.

Officials have been unable to turn the April ceasefire into a deal to permanently end the conflict, particularly as Israel intensifies and expands its military campaign in Lebanon against the Iranian-backed militia Hezbollah.