WASHINGTON -- Secretary of State Mike Pompeo said renewed U.S. sanctions on Iran will be rigorously enforced and remain in place until the Iranian government radically changes course.

Speaking to reporters aboard his plane on his way home from a three-nation trip to Southeast Asia, Pompeo said Monday's re-imposition of sanctions is an important pillar in U.S. policy toward Iran. He said the Trump administration is open to looking beyond sanctions but that would "require enormous change" from Tehran.

"We're hopeful that we can find a way to move forward but it's going to require enormous change on the part of the Iranian regime," he said Sunday. "They've got to behave like a normal country. That's the ask. It's pretty simple."

Get Breaking News Delivered to Your Inbox

Pompeo called the Iranian leadership "bad actors" and said President Donald Trump is intent on getting them to "behave like a normal country."

A first set of U.S. sanctions that had been eased by the Obama administration under the terms of the landmark 2015 Iran nuclear deal will take effect again on Monday, following Trump's May decision to withdraw from the accord. Those sanctions target Iran's automotive sector as well as gold and other metals.

A second batch of U.S sanctions targeting Iran's oil sector and central bank will be re-imposed in early November.

Pompeo noted that the U.S has long designated Iran as the world's foremost state sponsor of terrorism and said it cannot expect to be treated as an equal in the international community until it halts such activities.

"Perhaps that will be the path the Iranians choose to go down," he said. "But there's no evidence today of a change in their behavior."

In the meantime, he said, "we're going to enforce the sanctions."

Iranian Foreign Minister Mohammad Javad Zarif expressed his frustration to journalists on Monday.

"American bullying and political pressures may cause some disruption, but the fact is that in the current world, America is isolated," the semi-official ISNA news agency reported him saying.

The European Union also voiced its disapproval.

"We deeply regret the re-imposition of sanctions by the US," EU diplomatic chief Federica Mogherini said in a statement jointly signed with British, French, and German foreign ministers.

"We are determined to protect European economic operators engaged in legitimate business with Iran," the statement said.