Secretary of State Mike Pompeo speaks during a media briefing at the State Department June 10, 2019 in Washington, DC.

The U.S. State Department called on American citizens to "exercise increased caution" while traveling to Saudi Arabia, a travel advisory posted on its website said on Wednesday.

U.S. Mission personnel and their families are not permitted to use the airport in Abha without Chief of Mission approval, the note added. Abha airport has been frequently attacked by drones and missiles launched from Yemen, where a Saudi-led coalition has been battling the Houthi group.

Saudi Arabia's largest oil plants were targeted in drone and missile attacks early Saturday morning that knocked out more than half of the kingdom's global daily exports. Authorities told the public that the ensuing fires were contained and there were no casualties.

The facilities hit — Abqaiq, world's largest oil processing facility and crude oil stabilization plant and Khurais, the country's second-largest oilfield — are located in Saudi Arabia's oil-rich Eastern Province.

While Yemen's Houthi rebels, who have been at war with the Saudis since 2015, claimed responsibility for the attack, numerous officials and analysts point to Tehran. U.S. Secretary of State Mike Pompeo via Twitter blamed Iran for the attack, saying "Iran has now launched an unprecedented attack on the world's energy supply." Tehran denies the claims.