Pompeo said the U.S. reached its conclusion based on intelligence and the types of weapons used in the attack.
"It is the assessment of the United States government that the Islamic Republic of Iran is responsible for the attacks that occurred in the gulf of Oman today," said the Secretary of State. "This assessment is based on intelligence, the weapons used, the level of expertise needed to execute the operation, recent similar Iranian attacks on shipping and the fact that no proxy group operating in the area has the resources and proficiency to act with such a high degree of sophistication."
"These attacks are a threat to international peace and security, a blatant assault on the freedom of navigation, and an unacceptable escalation of tension by Iran," wrote Pompeo on Twitter.
Earlier today, a U.S. official told CBS News that it was "highly likely Iran caused these attacks."
Iran claimed that it rescued 44 sailors from the two ships, an assertion the U.S. official says is "patently false."