U.S. President Donald Trump signed an executive order on Monday to enact sanctions targeting Iranian Supreme Leader Ayatollah Ali Khamenei and his office.

Trump said Khamenei has been “responsible for the hostile conduct of the regime.”

As such, he announced over the weekend that he would enact “major” sanctions.

“Iran cannot have Nuclear Weapons! Under the terrible Obama plan, they would have been on their way to Nuclear in a short number of years, and existing verification is not acceptable. We are putting major additional Sanctions on Iran on Monday,” tweeted the president.

U.S. Treasury Secretary Steve Mnuchin announced that the United States will sanction Iranian Foreign Minister Javad Zarif “later this week.”

The latest sanctions occurred as Iranian-allied Yemeni Houthi rebels killed one person and wounded seven in an attack on a Saudi Arabian airport on Sunday evening.

Trump called off retaliatory strikes against Iran last week for shooting down an American spy drone near the Strait of Hormuz, which Trump confirmed on Friday, saying that such a response was “not proportionate to shooting down an unmanned drone.”

Wednesday’s incident occurred less than a week after Iran allegedly attacked two tankers—one carrying oil and the other transferring a freight of methanol—in the Gulf of Oman near the strategic Strait of Hormuz. Iran has denied responsibility for the incident.