July 7 (UPI) — U.S. Central Command said Tuesday evening that it launched “a series of powerful strikes” against Iran in response to Iranian attacks on three ships in the Strait of Hormuz.

The attacks were “to impose heavy costs for targeting and attacking commercial shipping crewed by innocent civilians in an international waterway,” Central Command said in a social media post. “Iran’s demonstrated aggression was unwarranted, dangerous and a clear violation of the cease-fire.”

The United States also reimposed sanctions on Iranian oil sales in retaliation for the attacks. The Treasury Department revoked waivers allowing Iran to sell oil and petrochemicals, CBS News reported.

Iran said the sanctions were “in clear violation” of the memorandum of understanding to end the conflict between Iran and the United States that was signed in June. Iran’s Foreign Ministry said it “holds the U.S. government responsible for this breach of commitment,” CNN reported.

The ministry said the United States “has repeatedly committed both minor and major violations of various provisions of the” agreement over the past 20 days.

Iranian state media reported explosions in Bandar Abbas and Sirik. Iran had previously warned the United States and Israel not to launch any strikes during the funeral for Ayatollah Ali Khamenei, who was killed by U.S. attacks in February. The funeral is expected to last throughout this week.

The earlier strikes by Iran were on tankers that were allegedly trying to travel the strait by a route Iran has warned against, CBS News reported. While Iran did not claim the attacks, but state media said at least one ship ignored warnings.

U.S. President Donald Trump is in Ankara, Turkey, for a NATO summit, during which attendees were expected to discuss the Strait of Hormuz.