President Trump said Wednesday that he has ordered a substantial increase in sanctions against Iran, as tensions continued to escalate over strikes on the Saudi oil industry that the United States has linked to Iran.

“I have just instructed the Secretary of the Treasury to substantially increase Sanctions on the country of Iran!” President Trump wrote on Twitter, without elaboration.

The comment comes after Iranian news agencies reported that Iran warned the United States that it would broadly retaliate against any attacks in the wake of crippling drone strikes on the Saudi oil industry over the weekend.

It was not immediately clear what the increase in sanctions might entail.

Iran’s warning, which was sent via the Swiss Embassy in Tehran that handles U.S. affairs in the country, condemned remarks by Secretary of State Mike Pompeo and other officials linking Iran to the attacks on a Saudi oil field and processing facility.

“Iran’s response will be prompt and strong, and it may include broader areas than the source of attacks,” the Mehr News Agency reported the official note as saying.

Paul Schemm contributed to this report.