President Donald Trump ordered additional economic sanctions on Iran Wednesday, as he continues weighing how to respond to the drone attacks on Saudi Arabia oil production.

“I have just instructed the Secretary of the Treasury to substantially increase Sanctions on the country of Iran!” Trump announced on Twitter.

Trump acknowledged Monday it “looked like” Iran was responsible for the attacks, but said he would wait until they reached a definitive conclusion. He sent Secretary of State Mike Pompeo to meet with Saudi officials to discuss how to properly respond to the attacks.

The president has ratcheted up sanctions considerably on Iran after leaving the Iran nuclear deal reached under former President Barack Obama.

Trump said Monday he was not interested in meeting with Iranian President Hassan Rouhani during the United Nations Summit next week, despite appearing open to the possibility.

“I never rule anything out, but I prefer not meeting him,” he told reporters.